News this Week

Science  04 Oct 2002:
Vol. 298, Issue 5591, pp. 30

    Parasite Genome Sequenced, Scrutinized

    1. Elizabeth Pennisi

    Plasmodium falciparum packs a powerful punch. The protozoan parasite causes malaria in hundreds of millions of people, most living in Africa. Thus far it has ducked every vaccine attempt and shaken off most of the drugs developed to knock out the disease. But now P. falciparum's opponents have three new genome sequences in their corner, making them hopeful that they will put up a better fight in the next round. (See The Mosquito Genome, a special section that begins on page 77.)

    This week, an almost complete DNA sequence of P. falciparum, as well as a draft of the genome sequence of a related Plasmodium species that infects rodents and is used to learn more about its human counterpart, appears in Nature. And on page 129 of this issue of Science, other researchers are reporting the DNA sequence of Anopheles gambiae, the mosquito that most efficiently transmits P. falciparum to humans in Africa. Together with the human genome sequence, researchers now have in hand the genetic blueprints for the parasite, its vector, and its victim. This “will provide the ability to take a holistic approach in understanding how the parasite interacts with the human host,” says Alan Cowman, a molecular parasitologist at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia. With that approach, researchers say, new antimalarial strategies should be possible.

    Just as P. falciparum has shown no mercy in its long association with people, it also proved a tough opponent for researchers trying to decipher its 23-million-base genome. They encountered “surprisingly difficult problems,” says David Roos, a malaria expert at the University of Pennsylvania in Philadelphia. Indeed, it took dozens of people from four organizations—the Sanger Centre in Hinxton, U.K. (now called the Wellcome Trust Sanger Institute), The Institute for Genomic Research (TIGR) in Rockville, Maryland, the Naval Medical Research Center (NMRC) in Silver Spring, Maryland, and the Stanford Genome Technology Center in California—to get the job done.

    Malarial menace.

    Researchers have sequenced the genome of Plasmodium falciparum (dark spots inside red blood cells).


    When the project began in 1996, the sequencers were immediately stymied by the parasite's unusually high proportion of adenine and thymine, two of the bases that make up the DNA code. The chemical nature of these bases hindered efforts to chop the DNAinto large snippets that make wholesale sequencing and reassembling of each chromosome easier. Early on, the preponderance of adenine and thymine clogged up the computer programs designed to evaluate data quality and piece the DNA back together. And in another complication, the researchers were able to isolate the DNA for just 11 of the parasite's 14 chromosomes. They eventually treated the three remaining chromosomes as a “blob” that proved even more difficult to decipher.

    Chromosomes 2 and 3 were finished in 1998, and now another eight are complete, with four more—6, 7, 8, and 13—in the final stages. Even the incomplete code provided ammunition for malaria fighters. Now, with the sequence essentially known, as well as a draft of the P. yoelii genome sequence by a team led by TIGR, whole-genome analyses are providing a “much better appreciation for the complexity [of P. falciparum] and also its Achilles' heels,” says NMRC molecular biologist Daniel Carucci, a physician who helped coordinate the project.

    One Achilles' heel could be an odd subcellular component, called the apicoplast, found only in Plasmodium and its relatives. It seems to be derived from a chloroplast that had been appropriated from algae consumed by the parasite's ancestor. Ever since the apicoplast's discovery by Roos in 1997, malaria experts have been eyeing its proteins as possible drug targets. Researchers knew that the apicoplast was involved in lipid metabolism, “but we didn't know how,” says Roos.

    Now, thanks to the genome sequence, “we've been able to put together a complete metabolic pathway,” he says, and show that about 12% of all the parasite's proteins, once made, head for the apicoplast. This structure also appears to be the only place where the parasite makes the fatty acids it needs to survive. Thus, Carucci explains, “if one [could] target this biochemical pathway, one would have a drug-target strategy that would be highly effective against the parasite and would not affect humans.”

    Malcolm Gardner and his colleagues at TIGR are still trying to make sense of the sequence. P. falciparum appears to have about 5300 genes. The researchers are not yet able to identify the function of some 60% of these genes, they report. In addition, genes with related functions appear to be clustered on the genome, suggesting that they might share the same regulatory DNA.

    Even with unanswered questions, researchers are using the sequence to build a catalog of Plasmodium proteins and to make gene chips for molecular studies of different points in P. falciparum's life cycle. In the proteomics arena, at least two research groups report in Nature that they are using sophisticated mass spectrometry techniques to look at thousands of proteins and determine when in the parasite's life cycle they are active. For vaccine developers, who want to create defenses against all of the parasite's alter egos, “that's very valuable information,” says Gardner.

    In one proteomics study, Laurence Florens and John Yates of the Scripps Research Institute in La Jolla, California, and their colleagues examined more than 2400 proteins. They found that the protein complement of the sporozoite—the form of the parasite a mosquito injects when it feeds on human blood—was quite different from that of other stages of the life cycle. Almost half of the sporozoite's proteins were found nowhere else, they report. But there were also a few unexpected genes in common. Researchers had thought that the parasite made var proteins—used to evade the immune system—only while in human blood, but these studies have now shown that “they are expressed before it even gets to the host,” says Carucci.

    And in a separate evaluation of 1289 proteins, Edwin Lasonder and Matthias Mann of the University of Southern Denmark in Odense found 315 that are unique to the immature male and female gametes that enter the mosquito and 226 in the asexual stages. “Intellectually, it's very exciting to think we have a total catalog of the relevant genes for all the parts of the life cycle,” says Roos, who has set up a database ( to compile the onslaught of genomic data on Plasmodium.

    Harvard's Sarah Volkman and her colleagues, among others, are using the P. falciparum sequence to expand studies of drug resistance. As described on page 216, working with Elizabeth Winzeler of the Genomics Institute of the Novartis Research Foundation in La Jolla, California, Volkman's team built gene chips to detect genetic changes—or polymorphisms—between P. falciparum strains. “Drug resistance is bred by polymorphisms,” Winzeler explains. “So being able to actually determine where [the polymorphisms] exist allows you to study the spread of drug resistance.”

    Whether with more gene chips, proteomic studies, gene searches, or comparative genomics, other malaria experts are eager to make use of the newly sequenced mosquito and Plasmodium genomes. “There are going to be fantastic strides in the years to come,” says Thomas Wellems, a malaria expert at the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. “I have no doubt that a deeper understanding of the biology of the parasite is going to lead us to better therapies.”


    Gene Therapy a Suspect in Leukemia-like Disease

    1. Eliot Marshall

    A French gene-therapy team that was hailed in 2000 for its breakthrough in curing children of a lethal immune deficiency reported a serious adverse event this week. One of 10 children they treated has developed a blood disorder resembling leukemia. Concerned that the therapy might have caused the problem, researchers Alain Fischer and Marina Cavazzana-Calvo of the Necker Hospital in Paris have halted the trial and urged others who use similar methods to hold off until the risks are assessed. At press time, French regulatory officials were preparing a public advisory.

    Fischer says he and his group recognized the importance of the case “exactly 1 month ago” but decided to study it and explain it to their patients before going public. The French team quickly sent advisory letters to investigators in charge of similar gene therapy trials using gene transfer “vectors” made from a retrovirus called the mouse Moloney leukemia virus. When the warning reached the U.S. National Institutes of Health (NIH) in Bethesda, Maryland, a clinical group immediately cancelled a six- patient trial due to begin in September.

    This French trial was designed to identify children with a type of severe combined immunodeficiency (SCID) caused by a mutation on the X chromosome and to treat them early (Science, 28 April 2000, p. 669). So far, the team has treated nine infants and one teenager. All faced the prospect of lethal infections or harsh therapy such as bone marrow transplantation, which itself often has fatal consequences. Gene therapy offered a way out; in most cases it restored the immune system without toxicity.

    During a routine check of their fourth patient last spring, however, the French researchers noted that the child had a high number of γδ T cells in his blood. The import didn't hit home until late August, Fischer says, when the T cell count climbed “very high”—to 200,000 cells per microliter. Other symptoms also appeared, including mild anemia, and the child was hospitalized.

    Molecular studies revealed that the T cells were monoclonal: All had come from a single cell. Furthermore, Fischer explains, all the cells contained the same DNA signature, a sequence reflecting the site where the retrovirus vector had integrated itself into the host's genome. “Unfortunately,” Fischer says, that site is in the coding region of a gene on chromosome 11 that's “aberrantly expressed” in a form of childhood acute lymphoblastic leukemia.

    Fischer believes that the vector triggered “an insertional mutagenesis event”—splicing itself into a dangerous gene and stepping up its production. “Everyone was aware” of a theoretical risk that retrovirus vectors might do this, he says, but the risk seemed very small. The phenomenon did not turn up in animal experiments or in other clinical data.

    Although gene therapy probably contributed to the patient's T cell response, Fischer says, other factors probably played a role, too. For example, the child might have been predisposed to disease, as other members of his family have had childhood cancers. And an infection might have been important as well; the child got chickenpox shortly before his T cell count spun out of control. But at the moment, Fischer acknowledges, it's not clear whether this was a “very unlucky” random event or a sign that the risk of using retrovirus vectors has been “underestimated” in the past.

    Researchers at the Necker Hospital are collaborating with Christof von Kalle of the Institute for Molecular Medicine in Freiburg, Germany, to try to create a map of all known human DNA integration sites for this retrovirus vector. They hope this will enable them to estimate the risks better. Meanwhile, the child is receiving chemotherapy.

    Few gene-therapy researchers were available to comment on the case at press time. But Jennifer Puck, a leader of the planned SCID therapy trial at NIH, knows of four other groups that are using or were planning to use similar gene-therapy techniques. At the moment, she says, “we don't know whether the risks [of insertional mutagenesis] are one in 80 or one in 10 million.”

    U.S. regulatory officials declined to comment on the case. But NIH's Recombinant DNA Advisory Committee is reported to be preparing a broad review of the case at its next meeting, scheduled tentatively for 4 to 6 December.


    Georgia County Opens Door to Creationism

    1. Constance Holden

    The forces of creationism gained ground in Georgia last week when a local school board unanimously adopted a policy that opens the door to creationist-inspired critiques of evolution in biology classes. The policy follows the board's decision in March to insert “disclaimers” into new elementary and high school biology textbooks saying that evolution is only a “theory.” The action directly affects only 95,000 students in Cobb County, a suburb of Atlanta and the 28th largest school district in the country. But many science educators say it is part of a national campaign to teach creationist ideas alongside evolution for the sake of “balance.”

    The new policy, approved 27 September by a 7-0 vote, asserts that “discussion of disputed views of academic subjects is a necessary element of providing a balanced education, including the study of the origin of the species.” It goes on to say that the policy is intended “to foster critical thinking among students [and not] to restrict the teaching of evolution [or] to promote or require the teaching of creationism.” It supersedes a 1995 policy stating that instruction relating to the origin of life should be conducted with “respect” for the “family teachings” of Cobb County citizens.

    The vote was preceded by an intense publicity and lobbying blitz from scientists, including a letter from National Academy of Sciences president Bruce Alberts urging the academy's Georgia members to speak out against the measure. Scientists from most of the state's colleges and universities also submitted petitions. The Seattle-based Discovery Institute, creationism's main think tank, has been recirculating a year-old statement signed by 130 scientists nationwide, as well as a new one signed by 28 Georgia scientists, expressing “skepticism toward the Darwinian claim that ‘random mutation and natural selection account for the complexity of life.’”

    Going critical.

    Jeffrey Selman, who has sued the board for adding disclaimers to textbooks, refrains from joining applause for the board's latest attempt to provide a “balanced education.”


    It's not clear what the practical impact of the new policy will be. School board chairperson Curtis Johnston Jr. could not be reached for comment, but last month he told the Atlanta Journal-Constitution that the board proposed a revision to “clarify things” for teachers who are “nervous about what they can talk about.” Cobb County's high school science supervisor George Stickel is even more opaque. Until school officials draw up regulations to implement the new policy, he says, “your guess is as good as mine” about how it will affect students. But he hopes that teachers will use the issue as “an educative moment.”

    Those who oppose the new policy see it as a signal to district parents who are sympathetic to creationism or “intelligent design.” Ronald Matson, a biologist at Kennesaw State University in Marietta, says that the resolution “fails to discriminate between science and nonscience ways of knowing … [thus] opening the doors to those with a creationist view to demand equal time.” Wes McCoy, a science teacher at North Cobb High School, says that many regard it as a “nod” to creationists, one that says, “even though we cannot teach it, we kind of wish we could.”

    The Supreme Court ruled in 1987 that creationism has no place in science classes; since then, evolution foes have taken the tack that students need to be informed of the “scientific” controversies surrounding evolution. Jeffrey Selman, a Cobb County parent who is challenging the board's textbook disclaimers as a violation of the constitutional separation of church and state, says that he plans to add the new policy to his federal suit, filed 21 August.

    Meanwhile, conflicts over evolution are simmering on other fronts. An Ohio committee developing new science teaching standards is also being asked to allow teachers to “teach the controversy.” The panel meets 14 to 15 October to prepare a recommendation to the state board of education. And in Kansas, two moderates lost their primary bids this summer to remain on the state board of education, improving the chances that conservatives could capture half of the seats in the November general election. The board attracted national attention in 1999 after taking a pro-intelligent design stance that was rescinded by the current board.


    Japanese Societies Tackle Gender Issues

    1. Dennis Normile

    TOKYO—Next week some 30 national academic societies will meet here to tackle a subject they have been slow to examine: the dearth of women in the scientific and engineering work force. The meeting marks the debut of a coalition on gender issues that could be a powerful force for change, say advocates, if it's willing to address tough issues such as sexual harassment and a glass ceiling for managers.

    The nascent organization, which doesn't have an English name yet, represents more than 100,000 working scientists in disciplines from basic physics to mechanical engineering to architecture. “Given the size of their memberships, they should be able to produce results,” says Mariko Kato, an astrophysicist at Keio University in Yokohama and a longtime activist in the effort to improve conditions for women scientists. “But I'm waiting to see what they do next.”

    The new focus on gender issues in science in Japan traces its origins to a committee of the Japan Society of Applied Physics (JSAP), which last fall surveyed its 23,000 members about working conditions, job satisfaction, and balancing career and family responsibilities. The survey confirmed a lot of common suspicions: Men climb career ladders faster and go higher than women (see graph). Men spend more time on the job and do less housework, particularly during their 30s and 40s. Male researchers in their 40s and 50s are more likely to be married and have more children than their female counterparts, suggesting that women tend either to drop out of the work force to raise families or to eschew a family to focus on their career. Both men and women overwhelmingly want a better balance between work and family responsibilities.


    Subsequent discussions within the committee and at small symposia have focused on issues raised previously by other groups (Science, 2 February 2001, p. 817; 20 April 2001, p. 416). They include the need to examine regulations and unwritten customs that make it difficult for women to reenter the scientific work force after having children, the value of child care leaves for men, and the importance of having women on research teams and as managers of large projects.

    The JSAP committee decided that there was strength in numbers. “We realized there is no point in each society pursuing such activities on its own,” says Kashiko Kodate, a physicist at Japan Women's University in Tokyo, who chairs the committee. JSAP contacted the Physical Society of Japan, the Chemical Society of Japan, and several other academic groups, which drew up plans for next week's formation of a liaison council. Their combined membership has caught the eye of a long list of politicians and government officials, who will offer statements of support. Participants are expected to adopt a resolution calling on government, industry, and academia to address gender-equity issues.

    Kazuo Kitahara, a physicist at International Christian University in Tokyo and current president of the Physical Society, admits that the group's goals and how to pursue them “are still under development.” But he agrees that it needs to move toward framing concrete proposals. “If the liaison council could produce some definitive resolutions, that would have a big impact on the Ministry of Education and also the national universities,” he says. “I think the council should move in that direction; otherwise it will just be [another group] holding meetings.”


    White House Adviser Tapped to Head FDA

    1. Jennifer Couzin

    After 20 months without one, the U.S. Food and Drug Administration (FDA) might soon have a new boss. Last week, President George W. Bush announced his choice for the next commissioner: Mark McClellan, a 39-year-old economist, physician, and current White House adviser. McClellan has impressive bipartisan credentials—he comes from a prominent Texas Republican family and has occupied posts in both the Clinton and Bush Administrations—but he has never run anything like the 10,000-person FDA, which governs everything from pharmaceutical products to genetically modified food.

    The FDA appointment has been mired in politics since President Bush took office. Democrats such as Senator Edward Kennedy (D-MA), chair of the panel that screens the nomination for Senate confirmation, let it be known that they would oppose any candidate with close ties to the pharmaceutical industry. At the same time, some conservatives reportedly were looking for a nominee who would halt sales of the “abortion pill,” RU-486.

    McClellan apparently has no industry ties, and it's not known how he will respond to the RU-486 controversy, but friends and co-workers say they can't imagine a more able candidate. “One of the things he'll bring [to FDA] is a great sense of fairness and pragmatism,” says Alan Garber, director of the Center for Health Policy at Stanford University, where McClellan worked for several years. “He's not an ideologue by any means.” McClellan declined to comment before being confirmed.

    New prescription.

    Mark McClellan is an economist and physician.


    McClellan's career has crossed many boundaries. He studied economics at the Massachusetts Institute of Technology (MIT) while enrolled in a joint Harvard-MIT medical training program. After a medical residency in Boston, he relocated to Stanford University, where he treated patients, advised medical school students, and conducted research on a favorite subject: the economics of medical technology. In 1998, he was appointed deputy assistant secretary for economic policy at the U.S. Treasury under then- President Bill Clinton, where he spent much of the time advancing the Administration's policy on Medicare reform. Currently, he sits on the Council of Economic Advisors.

    FDA, though, doesn't deal much in academic issues. It faces an array of practical challenges, including an overhaul of its food safety division for improved biodefense; concerns about how to protect human subjects in drug trials; new worries about West Nile virus contaminating blood and transplanted organs; and a long-running budget battle. Without commenting on McClellan, FDA senior associate commissioner Murray Lumpkin confirms that the agency is confronting an unusual set of new obligations.

    Those who know McClellan have no doubt he'll rise to the challenge. “He is gifted at searching out the room in the center where a compromise can be struck,” says a former colleague at the Treasury Department. “I have zero concern about his ability to manage that agency.”

    One of McClellan's unique traits, says longtime friend and Harvard economist David Cutler, is his willingness to let the data overcome personal biases, as in a paper the pair produced showing that the benefits of new technologies to treat heart attacks outweighed their high cost—contrary to their expectations.

    Cutler acknowledges, though, that McClellan probably wouldn't enjoy the “very political parts of the job,” which might be “the things he'd do worst at or like the least.” But Cutler and others who have worked with McClellan are convinced that his wide-ranging gifts will offset any shortcomings.


    Scientists Blast Budgetary Bad News

    1. Barbara Casassus*
    1. Barbara Casassus is a freelance writer in Paris.

    PARIS—If the phrase “lies, damn lies, and statistics” hadn't already been coined, French researchers might have been tempted to do so last week when the government unveiled competing versions of its civil R&D budget for 2003.

    Figures released by the Finance and Research ministries paint strikingly different pictures. According to the Finance Ministry, the 2003 budget would shrink by 0.8% to € 8.65 billion—from € 8.72 billion in 2002—whereas the Research Ministry has it rising by 1.4% to € 8.84 billion. SNCS, a leading researchers' union, contends that the budget is in fact going down, and by week's end it had collected signatures from more than 1000 lab chiefs and rank-and-file scientists on a petition claiming that the cuts would have a “severe impact on the dynamism of our research.”

    The bizarre budgetary duet played out at the annual budget press conferences here last week. At the Research Ministry's unveiling, new minister Claudie Haigneré claimed that the R&D budget was even healthier than the numbers indicated, as her ministry intended to carry over “very probably more than” € 720 million in unspent cash from 2002, thus raising the budget by 5.3%. The former astronaut's budgetary magic dazzled—and befuddled—a room full of journalists. “Is the budget up or down; is it a success or a failure?” asked one anguished reporter.

    Analyses suggest that the finance figures are nearer the truth. The Research Ministry's projected gains include € 250 million next year in extra budgetary authority, including the French Petroleum Institute's € 200 million budget and money from a handful of other programs. Moreover, much of the funds that Haigneré intends to carry over are not under her control, asserts SNCS secretary-general Jacques Fossey. “More than half belongs to the laboratories; the public research institutes merely act as bankers,” he says. By SNCS's calculations, the 2003 figure is a 1.3% drop, or about 3% after inflation.

    Even though rumors of a 7.6% cut in civilian R&D proved unfounded, many scientists are furious. “This is one of the most catastrophic research budgets we have had in living memory,” says chemist Henri Audier, a board director of the basic research agency CNRS. Spending on research grants would fall by 11% overall, with CNRS absorbing a 17% hit. “It will be very difficult to launch any new projects without sacrificing existing ones,” Audier says. In another sleight of hand, the draft budget—which must be approved by parliament—would create 400 temporary (18-month-long) postdoc positions at the institutes while scrapping 150 permanent posts. Universities would fare a bit better, winning an extra 420 positions for lecturers and professors.

    “In France,” grouses one researcher, “every time the right comes to power, research is one of its first victims.” That characterization, however, is rejected by Prime Minister Jean-Pierre Raffarin. “You will see that we will invest more in research in 2003 than in 2002,” he claimed in a television interview. Haigneré, meanwhile, insists that the draft budget is “transparent and true.” Observers expect the budget to pass with minor tweaks later this year.


    Cloning Pioneer Heads Toward Human Frontier

    1. Gretchen Vogel

    BERLIN—The father of Dolly the lamb is hoping to blaze a new trail in the science of cloning: He plans to apply the technology in the controversial arena of human embryonic stem cell research. In a briefing for journalists here last week, Ian Wilmut, leader of the team at the Roslin Institute in Edinburgh, U.K., that 6 years ago produced the world's first mammal cloned from an adult cell, announced that his group will attempt to use nuclear transfer to create human embryos that are genetically identical to adult donor cells. These embryos would then be tapped for stem cell lines.

    Wilmut and his team are not the first out of the blocks to try nuclear transfer experiments with human tissue, but they appear to be the first to test the United Kingdom's new procedures for approving such studies. The creation of cloned embryos is allowed in the U.K. as long as a license is obtained from the U.K.'s Human Fertilisation and Embryology Authority (HFEA). An HFEA spokesperson confirms that Wilmut's group would be the first to apply for a license. So-called reproductive cloning—implanting a cloned human embryo into a surrogate mother—is illegal in the United Kingdom and is not being contemplated by Wilmut.

    Pushing forward.

    Ian Wilmut wants to clone human cells.


    Several teams have attempted nuclear transfer using human embryos in secret—with little apparent success. Advanced Cell Technology (ACT), a biotech firm in Worcester, Massachusetts, reported last year that its scientists had produced early embryos but no blastocysts and therefore no stem cells (Science, 30 November 2001, p. 1802). Roger Pedersen, now at Cambridge University, used private funding to attempt human nuclear transfer experiments when he was at the University of California, San Francisco, but he too failed to produce blastocysts. And newspapers have reported that scientists in China are attempting human cloning experiments, but peer-reviewed results have not yet emerged.

    Wilmut, who was in Berlin to receive the Ernst Schering Prize for his nuclear transfer work, says he expects the licensing process to take about a year. The proposal must undergo rigorous reviews by at least four ethics committees and must be approved by HFEA's scientific and clinical review boards. The oocytes would be collected from women who are planning to undergo reproductive-tract surgery, Wilmut says, and donors would not be compensated.

    The team's first goal is to create stem cell lines that could help researchers understand complex genetic maladies such as heart disease, Wilmut says. If cells from a cardiac patient could be cloned and a stem cell line created, for example, researchers could grow those cells into cardiomyocytes and perhaps learn more about what causes sudden heart attacks as well as possible ways to prevent or treat the condition. Wilmut says his team will not use human cells to shed light on the murky mechanisms governing how an adult-cell nucleus can be reprogrammed to direct embryonic development. Such work, he says, can be done in mice and cattle, from which oocytes are much easier to obtain.

    Wilmut's research will be supported by Geron Corp. of Menlo Park, California, which funded much of the early work on embryonic stem cells and Pedersen's experiments with human nuclear transfer. Geron, through its acquisition of Roslin's spinoff company, Roslin Bio-Med, owns several patents on the techniques used to create Dolly. The company also claims exclusive commercial rights to several cell types derived from embryonic stem cells, including cardiomyocytes.

    Other experts welcome Roslin's plans. “The scientific rigor of what Roslin produces” would give the field a boost, says Robert Lanza, vice president of medical and scientific development at ACT. Gerald Schatten of the University of Pittsburgh, whose efforts to clone rhesus monkeys have been stymied by faulty cell division in the resulting early embryos, predicts that human cloning, at least to the blastocyst stage, will be feasible. “Everything to date suggests that there are hurdles in cloning Old World primates, including humans, but there is no reason to think it will not eventually work,” he says.


    Diagnosis and Rx for U.S. Coral Reefs

    1. Elizabeth Pennisi

    For more than a decade marine biologists have bemoaned the decline of coral reefs worldwide, citing global warming, disease, overfishing, and pollution, along with other causes (Science, 25 July 1997, p. 491). But good data have been scarce. Last month, a 5-year volunteer census of global reefs revealed more damage than expected (Science, 6 September, p. 1622). Now comes the most comprehensive look at U.S. reefs—and it, too, confirms many of the biologists' worst fears.

    The report, The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2002,* substantiates the degradation by various insults. It includes a breakdown of the problems facing 13 regions and some 20,000 square kilometers that come under the purview of the United States, as well as reefs surrounding its former territories Micronesia, the Marshall Islands, and Palau.

    “It is the most sweeping statement of concern by a [U.S.] federal agency about the trajectory of coral reefs to date,” says John Ogden, a marine biologist at the Florida Institute of Oceanography in St. Petersburg. Even so, comments Phillip Dustan, a marine biologist at the College of Charleston, South Carolina, “the report doesn't go far enough” in conveying the dire condition of reefs or the need for more research on their problems.

    Guardians wanted.

    U.S. policy-makers are pushing for protection of coral reefs (top) and their denizens such as blue tang (bottom).


    The effort dates back to 2000, when Congress, in the Coral Conservation Act, charged the 2-year-old interagency U.S. Coral Reef Task Force with producing a comprehensive inventory of reefs under U.S. jurisdiction. At the same time, Congress showed its increased concern for reefs by expanding federal support for reef research from $60.9 million in 1999 to $98.5 million in 2001, making such a survey possible.

    The National Oceanic and Atmospheric Administration (NOAA), the U.S. Agency for International Development, the Department of the Interior, and about a half-dozen other agencies have now produced summaries of current conditions of reefs, projections for their futures, conservation efforts, and descriptions that focus on each region. As with other reports, this one highlights the rampant destruction of some reefs by disease, overfishing, pollution, storms, and global warming. The report “has brought all this [reef] information together in one place for people to see,” says NOAA Administrator Conrad Lautenbacher.

    In addition, in the works is an atlas of digital, color-coded maps of undersea habitats such as sea grass and sand as well as reefs. These maps are being made from high-resolution aerial photos.

    An accompanying report to Congress outlines 13 goals based on the new assessment. First on the list are more mapping and monitoring projects. Eight of the goals are concerned with reducing the damage done by people.

    Ogden, for one, says these priorities should be reversed: “I believe it should be action first and research second.” Lautenbacher is not swayed by this criticism, however. First and foremost, the agencies need the key baseline inventory that only mapping and monitoring can provide, he insists. But he also points out that now that the task force has proposed a unified strategy for protecting coral reefs where once there was none, it can now be debated and changed as needed.


    NIH Grantees: Where Have All the Young Ones Gone?

    1. Erica Goldman,
    2. Eliot Marshall

    Since 1980, the percentage of biomedical grants awarded to 35-and-under investigators has plummeted from 23% to 4%

    Douglas Robinson, like his peers, spent his 20s in training. After 5.5 years in graduate school, he received a Ph.D. in cell biology and then worked another 4.5 years as a postdoc under a faculty mentor. When he was 31, he got an appointment at Johns Hopkins School of Medicine in Baltimore, Maryland, enabling him for the first time to apply for his own funding to investigate his ideas. His initial application to the National Institutes of Health (NIH) didn't get funded, but he hopes his second try will. If he succeeds, he will join a select—and vanishing—group: those who win NIH grants before age 35.

    In 2001, NIH gave out 6635 “competing” grants to investigators, but only 251 of them went to people age 35 or younger. This was slightly more than the year before (see graph below). But the 35-and-under group was much larger a decade ago and dramatically larger 2 decades ago. According to statistics released last month by NIH's deputy director for extramural research, Wendy Baldwin, the percentage going to the youngest age group has declined steadily, from 23% in 1980 to below 4% last year. Meanwhile, as Congress has pumped funds into doubling NIH's budget, the share of grants to scientists age 46 and older has grown sharply.


    The number of traditional NIH grants awarded to young investigators has declined, while those to researchers over 46 have grown.


    The trend is not new, nor has it gone unnoticed. But when biomedical leaders examined similar data in the early 1990s, they perceived a crisis. The National Research Council (NRC) launched an inquiry that produced two reports, one in 1994 and another in 1998. The authors called on government agencies to collect more data on young scientists and break the logjam that keeps many waiting until their 40s for an academic position. The 1994 report warned that “the implications … for the future of biomedical research are extremely serious.”

    The panel's co-chair, biologist Torsten Wiesel of Rockefeller University in New York City, is surprised to learn that this aging trend continues today: “You'd think with all the money that's going into NIH, [young scientists] would be doing better.” His co-chair, biologist Shirley Tilghman, now president of Princeton University, says simply, “It's appalling.” The data reviewed by the panel in 1994 looked “bad,” she says, “but compared to today, they actually look pretty good.” She adds: “The notion that our field right now has such a tiny percentage of people under the age of 35 initiating research … is very unhealthy and very worrisome.”

    Of course biologists are worried, Baldwin says: Their concern stems from “the long-held observation that a lot of people who do stunning work do it early in their careers.” Baldwin says it's precisely because NIH wants to keep on top of the situation that “we crank out stats” like these. But she does not think that the trend has a simple explanation. Biologists typically spend more years than physicists floating between graduate school and full employment, but biomedicine also offers more job opportunities. And although some people blame NIH for creating this situation, Baldwin notes that NIH does not control employment decisions in academia.


    Experts differ on why older biomedical researchers are receiving a growing share of the pie these days and on what should be done about it. But they agree on the basic problem: The system is taking longer to launch young biologists.

    The 1994 data looked “bad, but compared to today, they actually look pretty good.”—Shirley TilghmanCREDIT: DENISE APPLEWHITE/PRINCETON UNIVERSITY

    Many observers see danger in this pattern. The long wait for independence takes a heavy toll on the individual, says evolutionary biologist Michael Cummings of the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, who participated on the committee that produced the 1998 NRC report. Many scientists must now work until midlife before they can obtain a stable income and clear benefits. It's tough on families, he says. “The whole system is plugged up,” says Joan Lakoski, assistant vice chancellor of career development for health sciences at the University of Pittsburgh. She's worried that young people might “vote with their feet” and leave for jobs that recognize talent earlier.

    But why is the pool of young investigators shrinking? It's not because the peer-review system is biased against younger people, Tilghman argues. When her NRC panel looked into this, she says, “we could find no data at all [supporting the idea] that young people are being discriminated against.” Baldwin suggests that young scientists are spending more time in training because biology has become more complex, and that is why they don't apply for grants until later. Marvin Cassman, a former NIH official who now heads the Institute for Bioengineering, Biotechnology, and Quantitative Biomedicine in San Francisco, seconds that view, saying, “You do have to take account of the increasing complexity of science.”

    Some say the trend reflects demographics and the tendency for professors to stay longer on the job now that mandatory retirement rules have been scrapped. There are fewer positions available in universities, says William Brinkley, vice president and dean of the Graduate School of Biomedical Sciences at Baylor College of Medicine in Houston, Texas. There was a boom of academic faculty hires in the 1960s, he says; jobs will open up when these scientists retire or go to the “happy laboratory in the sky.”

    Older Ph.D.s.

    The median age of Ph.D. awardees in the biological sciences has climbed since 1970.


    But the decline in the number of awards to young investigators illustrates more than a demographic shift, says Orfeu Buxton, a University of Chicago postdoc and one of the founders of the fledgling National Postdoctoral Association. “It clearly reflects the lengthening of the postdoctoral on-the-job training period over the last several decades,” he says. The postdoc has become an “obligatory credential, necessary but not sufficient to establish a young investigator's potential for other independent research jobs.”

    Frank Solomon, a cell biologist at the Massachusetts Institute of Technology in Cambridge, agrees. Solomon, co-author of a major study of biomedical training, says, “We interviewed postdocs in 20-odd prominent laboratories,” and “virtually all” said they were functioning as research scientists and not getting training. The plight of postdocs is “deplorable,” says Mary Golladay, program director for the Human Resources Statistics Program in the Division of Science Resources Statistics at the National Science Foundation (NSF). “NSF has been concerned about this for 15 years.”

    According to NSF data, there were 28,688 postdocs in the biological and health sciences in 2000. (Typically, biologists can spend four or more years in postdoc positions now.) The count has risen since 1993, at a rate of about 750 postdocs per year. In contrast, there were only 5880 postdocs in the physical sciences (chemistry, physics, and astronomy) in 2000, a number that has remained stable since 1993. Patrick Mulvey of the American Institute of Physics also found, in a survey of the 1999–2000 class of Ph.D.s, that 52% of physicists said they expected their postdoc term to last only 2 years; another 28% said it would last 3 years.

    Although NSF doesn't specifically target young investigators for grants, it does offer support to “teacher-scholars,” including the Presidential Early Career Awards for Scientists and Engineers, designed to recognize and bolster people off to an impressive start. NIH doesn't earmark grants for young investigators either but asks reviewers to give special attention to proposals from first-time applicants. Baldwin says that in recent years NIH has increased funding for these grants to first-timers.

    The United States is not alone in struggling with a system that makes scientists wait until their late 30s before they can establish an independent career. In Germany, the average age at which scientists receive their first grants from the German Research Council (DFG) is 40.4. But, in contrast to U.S. agencies, DFG has awarded a stable 10% of its grants in the under-35 category over the past 5 years.

    DFG, according to Beate Scholz, program director for the promotion of young scientists, wants to pave a path to scientific independence at a younger age and has helped set up a number of funding schemes to make this possible. At INSERM, the French equivalent of NIH, a program launched last year called Avenir offers strong financial support to promising scientists as they transition from postdoc to independent investigator. The various research councils in the United Kingdom have taken similar steps to draw talented people into the sciences and help them launch successful careers.

    What to do?

    No one doubts that the U.S. drift toward giving a larger share of funding to older investigators in biology should be reversed. “But people don't want to change a system that has seen a lot of success scientifically. And there is no magic button to push,” says MBL's Cummings.

    Tilghman is convinced, however, that the government should take the initiative: “I think there is a real failure of leadership at the NIH,” she says. Tilghman claims that grantees are hiring young scientists as cheap labor. To end this practice, she argues, NIH grants should help establish a career track for technical workers in the lab, one that would offer “reasonable salaries” and benefits. She thinks this would help by reducing some of the competition for tenured academic positions.

    Population shift.

    More young biologists (1 to 3 years post-Ph.D.) hold postdocs than faculty positions.


    NIH's Baldwin says that, to the extent the problem reflects a lack of job opportunities in academia, “that is something the universities have to deal with. We don't have any control over it.” She notes that NIH has taken some steps to improve postdocs' welfare. It has increased the stipends of 7500 postdoc fellowships it funds by 10% in each of the last 2 years, and it aims to raise them 10% a year through 2006.

    Postdocs, meanwhile, are taking matters into their own hands. Across the country, postdoctoral associations are cropping up at universities. A newly formed National Postdoctoral Association, in collaboration with Science's Next Wave (, seeks to advocate for change on a national level. Geoff Davis, a software consultant and mathematics Ph.D. in Raleigh, North Carolina, has launched a large-scale survey to collect detailed information from the U.S. postdoc population—something NSF has not done—to help influence national policy.

    All these efforts may be needed. Cassman says he's beginning to think that, “if the trend continues, people will be applying for their first NIH grant the year before they retire.”


    Congress Puts the Squeeze on NSF's Oversight Board

    1. Jeffrey Mervis

    The National Science Board finds itself walking a political tightrope in a dispute between NSF and Congress over managing the growing foundation

    This year was shaping up to be a breakout season for the National Science Board, which oversees the National Science Foundation (NSF) and provides free advice to the government on national science policy. After toiling for a half-century in relative obscurity, the board seemed well positioned to capitalize on NSF's favored status among Washington politicians. In February NSF earned a gold star from the Bush Administration for its management prowess (Science, 8 February, p. 953), and both houses of Congress are pushing ahead with a bill that endorses doubling its budget (Science, 27 September, p. 2187).

    But so far there have been more headaches than hosannas for Warren Washington, who in May became chair of the presidentially appointed body. A senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, he hasn't had much time to bask in the foundation's reflected glory. Instead, he's become the board's chief navigator through a suddenly perilous political passage.

    His biggest challenge is to strike a compromise between NSF's director and Congress, which is weighing proposals that give the board greater resources and independence. Legislators want the board to more aggressively oversee the foundation, whose $4.8 billion budget might soon be growing rapidly, and the House has already approved some proposed changes. Its director, Rita Colwell, is adamantly opposed to these ideas, however, on grounds that the status quo has served the process well.

    The board is caught in the middle. Its initial reaction was quite negative (Science, 23 August, p. 1257). But recent interviews by Science with several members suggest that a substantial minority favors more authority and independence—although everybody wants to avoid doing or saying anything that might jeopardize NSF's chances for sustained budget growth. Several members also expressed concerns about Colwell's role in replacing the board's executive officer earlier this summer. Washington is trying to plot a course through these currents with the narrowest of mandates: He earned the job in a one-vote victory over University of Virginia computer scientist Anita Jones, the closest election for board chair in recent memory.

    Congressional attention of any kind is a novelty for the part-time board, a unique body created by the law that established NSF in 1950. Its 24 members, typically well-regarded researchers or administrators from academia and industry, are chosen by the president and confirmed by the Senate for staggered 6-year terms ( The board meets six times a year to approve large awards, generate the occasional report about scientific affairs of the day, and discuss long-term strategy. It also signs off on NSF's annual budget request to the president.

    Tag team.

    Board chair Warren Washington, with NSF Director Rita Colwell, testified before the Senate this spring on NSF's proposed 2003 budget.


    Legislators have worried for some time that the balance of power was tilting toward the director, threatening to weaken the board's ability to exercise proper oversight. At the same time, they were concerned about how NSF selects and manages large research facilities, reflecting complaints from constituents that their projects had been approved by the board but had not yet been included in NSF's budget request. After a hearing last year on the subject (Science, 27 July 2001, p. 586), the House in June passed a bill that tackles both issues, ordering the director to rank the various projects by priority after consultation with the board. The language was picked up in July by Senate appropriators, who called for “a more open and understandable process” of explaining how NSF chooses from the large number of requests that bubble up from the community and pass muster with reviewers.

    The Senate bill tightened the screws by creating a separate budget for the science board. Last month, two more Senate committees approved an NSF reauthorization bill that, in line with the earlier panel's wishes, would give the board authority to hire its own staff. The changes, says a Senate aide, are meant to shore up the board's oversight capability at a time when NSF's budget is poised to grow rapidly, and when corporate scandals such as Enron and WorldCom have made it clear that a board of directors should be more independent of the company's officers.

    The changes would damage the relation between the board and the director, says Colwell, a University of Maryland microbiologist who has served 4 years of a 6-year, presidentially appointed term. They would add bureaucracy, end the board's current practice of borrowing NSF staff for reports and short-term projects, and create a gap between board and NSF where none now exists. “Nothing is broken, and there's nothing to be rectified,” she told Science. “This relationship has been revisited several times, and every time the conclusion is the same: It works. I'm very happy with the way things work right now.”

    The board harshly criticized the proposed changes at its August public meeting, saying that they were unnecessary and potentially harmful. John White, chancellor of the University of Arkansas, Fayetteville, led the attack: “At first I thought they might be catastrophic. Now I think they're only redundant.” Board members also worried about the increased responsibilities and cost of managing their own affairs.

    But in recent interviews with several board members, Science has found guarded support for many of the suggested changes. “I absolutely think that there is very strong value in some of them,” says Jane Lubchenco, an ecologist at Oregon State University, Corvallis. “Both the scientific community and the NSF would be better served if the board were more independent.” Stan Jaskolski, a retired executive at Eaton Corp. in Cleveland, Ohio, says that the board now lacks the ability “to meet by itself, independent of the management of the foundation, … to discuss key emerging issues and challenges. The system is not broken, but we need to constantly seek to improve it.”

    Some board members say the recent departure of Marta Cehelsky, the board's longtime executive officer, points up the need for greater autonomy. Soon after Washington became chair, Colwell shuffled the board's staff. Cehelsky is now on leave at the Inter-American Development Bank in Washington, D.C., helping incorporate science into long-term planning, and longtime NSF staffer Gerry Glaser serves as acting executive officer. “I was disappointed when Rita decided to remove Marta,” says Diana Natalicio, president of the University of Texas, El Paso, and vice chair of the board. “We lost a person we respected, and one who had a lot of experience. That leaves a void.”

    Colwell says the move was made with Washington's approval. “It was time for a change,” she says. “We agreed that it was time for him to have his own staff.” Washington has a different recollection of events. “The idea of changing board personnel was her idea, and the change was made much faster than I would have wanted,” he says. “There was some period of transition, but it wasn't ideal.”

    Although Washington has spent 8 years on the board, the 66-year-old climate modeler says he's still a political naïf who faces a steep learning curve. Dispatched by the board last month to Capitol Hill to learn the legislators' intent, Washington spent most of the time listening. “He was trying to take our temperature,” says one House staffer. “He said that some board members think [the changes] are not a bad idea and that the board would continue to talk about it.” Washington's assessment is typically understated: “I'm impressed with how seriously people on [Capitol] Hill are taking the board's responsibility to oversee the foundation.”

    The board's penchant for secrecy has traditionally kept any conflicts bottled up within the board's home at NSF's headquarters in suburban Virginia. But that might be changing. In June the House called on the board to conduct more of its business in public, and Washington says he is already thinking about how to do that. “I want to go back to a time of greater openness in discussing controversial topics,” he says.

    Washington also takes a philosophical view of possible changes in the board's status. “I think that most of the board still feels that these changes aren't necessary,” he says. “But if they get adopted, we can live with them. The important thing is the increased funding for NSF. That's the big news.”

    The fate of both NSF's budget and the board's authority over it now rests with Congress, which must reconcile competing versions of both spending and authorization bills. Only then will Washington and the science board learn what they have to live with.


    Neutrino Hunters Borrow Military Ears--and Eyes

    1. Charles Seife

    Undersea listening devices and an aging spy satellite are helping physicists look for ultrahigh-energy neutrinos

    A decade ago, nobody was sure they even existed. Ultrahigh-energy neutrinos, almost-undetectable particles moving so fast that they can carry as much energy as a baseball pitch, were a theoretical possibility—nothing more. Nobody had any way to spot them, and nobody could even guess what an instrument designed to detect them would see.

    But that's ancient history. Now physicists are firmly convinced that Earth is constantly being bombarded by ultrahigh-energy neutrinos, which are part of the debris generated when extremely energetic cosmic rays slam into the atmosphere, water, or rock, creating showers of particles. The neutrinos could give physicists valuable clues to the source of the cosmic rays that spawned them—one of the most vexing unknowns in modern astrophysics.

    Several experiments that can sense ultrahigh-energy neutrinos are planned, but they are years away. However, scientists are already searching for the particles, thanks to military hardware designed to snoop on a Cold War enemy. Using data from sources such as a submarine-listening facility and an aging spy satellite, a handful of shoestring projects are quietly paving the way for higher profile efforts soon to come—and could well beat them to the punch.

    “They're extremely nice and cooperative,” says physicist Giorgio Gratta of Stanford University of his U.S. Navy benefactors, who have given his lab at Stanford and physicists at the Scripps Institution of Oceanography in La Jolla, California, access to a 250-square-kilometer array of underwater microphones, or hydrophones, based at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. During the Cold War, the U.S. and Soviet navies sprinkled such acoustic arrays throughout the world's oceans in hopes of tracking enemy submarines. Now Gratta and colleagues think they might pick up the much subtler acoustic waves generated when particle showers triggered by incoming neutrinos heat up seawater, causing it to expand.

    To make an audible click in the ocean, a neutrino must carry a huge amount of energy: 1016 electron volts (eV), enough, perhaps, to knock an ant into the air. Until recently, most astrophysicists didn't think such neutrinos existed; no cosmic rays packed enough of a wallop to create them. But in the past few years, cosmic ray observatories such as the HiRes project in Utah have shown, to scientists' surprise, that cosmic rays with energies of 1020 eV and above do exist (Science, 19 May 2000, p. 1147), although how they form and where they come from remain a huge mystery.

    “With the very existence of cosmic rays going out to 1020 eV, there have to be high-energy neutrinos out there, too. It's inescapable,” says John Learned, an astroparticle physicist at the University of Hawaii, Manoa, and a pioneer in the field of ultrahigh-energy neutrinos.

    High and low.

    A spindly satellite (top) and underwater microphones (bottom) are serving as makeshift particle detectors.


    Unfortunately, the current generation of neutrino detectors—Super-K, the Sudbury Neutrino Observatory, and other underground devices—are too small to see ultrahigh-energy neutrinos. To catch such rare particles interacting with matter, physicists need to watch an enormous patch of sky, ice, or water—the bigger, the better. That limitation gave Gratta an idea. The ocean, he mused, is plenty big—and the Navy already has listening posts in place. Gratta called the Office of Naval Research, the Naval Postgraduate School in Monterey, California, and other facilities in hopes of tapping into the flood of data coming in from those arrays. He eventually reached AUTEC personnel, and his team started listening for neutrinos.

    “The AUTEC array has been in place for 30-odd years, working beautifully,” says team member Mike Buckingham, an acoustician at Scripps. “It's quiet; it's fairly well shielded from shipping noise. You get natural sounds from surface processes, like breaking waves and bubbles, and biological sounds from marine mammals.”

    Right now, the team is calibrating the instrument and characterizing that background noise to figure out whether AUTEC is capable of picking up the sound of a passing neutrino. One technique involves dumping weighted light bulbs overboard and checking how the hydrophones pick up the pops when the bulbs implode, about 100 meters down. By calculating the energy and depth of the implosions, the team can measure the array's sensitivity. Such low-tech methods help make the AUTEC project a bargain, Gratta says. “It's extremely cheap. The budget for the last 2 years has been $5000.” A similar Russian project is under way off the coast of the Kamchatka Peninsula, Learned says.

    Even as scientists exploit the military's underwater ears, they also are taking advantage of eavesdroppers in space. The Fast On-orbit Recording of Transient Events (FORTÉ) satellite was designed at the Los Alamos and Sandia national labs and launched in 1997 to help enforce a nuclear test ban. But for neutrino hunters, the ungainly looking spacecraft is a “wonderful, fortuitous thing,” says Learned.

    FORTÉ is an enormous antenna designed to pick up electromagnetic pulses, such as those created when a nuclear weapon detonates. It also picks up lightning strikes and other brief pulses of electromagnetic energy, such as those given off by a neutrino particle shower. Nikolai Lehtinen and Peter Gorham of the University of Hawaii, Manoa, got access to the data from September 1997 through December 1999, when the relevant antennae failed. “In the database there are around 4 million events, and we're looking at these events, trying to distinguish them from lightning,” Lehtinen says. The team is focusing on electromagnetic waves issuing from the Greenland ice shelf. Limiting the search to signals from Earth's surface, Lehtinen explains, filters out air showers due to cosmic rays, which never survive long enough to hit the ground. Although it's too early to say for sure that Lehtinen has detected an ultrahigh-energy neutrino, there is a promising candidate event.

    Even if AUTEC and FORTÉ never spot a neutrino, they have given physicists a head start in their search to detect ultrahigh-energy neutrinos. “It would cost millions and millions of dollars to build these things,” Learned says. Even a null result will teach physicists about background noise that will affect future searches in the ocean or from high above Earth. And if they succeed, it will be an unexpected bonus from technologies designed to spot lumbering submarines and gigantic explosions rather than wispy particles.


    A Compromise on Floral Traits

    1. Kathryn Brown

    Biologists are looking beyond pollinators to more subtle influences to learn how colorful, shapely flowers evolved

    Late this summer, Candace Galen crouched in a Rocky Mountain meadow, watching bees dart from flower to flower. Most evolutionary ecologists would have admired this precise pollination dance—the close fit between bee and blossom. But Galen was waiting for a thief.

    A nectar thief, to be exact. Galen, an ecologist at the University of Missouri, Columbia, studies the alpine skypilot (Polemonium viscosum), a purple perennial wildflower. Her research shows that pollinating bees are not the only ones pursuing the flower. Small, stealthy ants also devour the flower's nectar—and inflict a surprising amount of damage in the process. In fact, Galen suggests that both bee pollinator and ant predator might have inspired the skypilot's shape. “We know that flowers are compromise structures,” Galen says. “And this is a good example.”

    “Compromise,” as Galen puts it, is fast becoming the new buzzword as researchers uncover the details of floral evolution. Many scientists have long explained flower fashions rather simply: From richly red bee balm to the cornflower's spiky crown, popular theory has gone, each flower has evolved the right color and shape to attract effective pollinators. The yucca plant, for instance, turns its flowers upward at dusk, to be pollinated exclusively by the yucca moth, which rolls up its heavy pollen like a snowball.

    But today, a growing number of scientists are looking for more subtle evolutionary forces—from nectar thieves and herbivores to environmental demands and developmental changes—that might also sculpt floral traits. “We're taking a more pluralistic view,” says evolutionary ecologist Sharon Strauss of the University of California, Davis. And they're raising some eyebrows in the process.

    Unpicky pollinators.

    Whether naturally shaped or experimentally altered, the flowers of a Mediterranean lavender were equally popular with pollinators.


    Some pollinators, according to the new work, might not deserve their starring evolutionary roles. Reporting last year in the Journal of Evolutionary Biology, Carlos Herrera of the Estación Biológica de Doñana in Seville, Spain, questioned whether pollinators really shaped the flowers of a Mediterranean lavender, Lavandula latifolia. Like all species in the mint family, this lavender wears a two-lipped corolla, or double-layered whorl of flower petals.

    If pollinators had driven the evolution of this floral shape, Herrera reasoned, they should strongly prefer it. So with fine scissors and a magnifying glass, he snipped away either the upper, or most of the lower, corolla lip in roughly 300 flowers, leaving an additional 300 as natural two-lipped controls, at a field site in southeastern Spain.

    To his surprise, Herrera found that the pollinators weren't picky: They frequented the misshapen lavender flowers as often, and pollinated them as successfully, as the two-lipped variety. He concluded that today's bees, butterflies, and insects did not “selectively choose” the lavender's distinct floral style. Instead, Herrera argues, the entire mint family likely developed the two-lipped corolla long ago, before lavender met up with these modern pollinators. “There is an urgent need to critically reevaluate some mainstream ideas” about the all-importance of current pollinators in deciding floral traits, he says.

    In other settings, researchers are paying closer attention to uninvited floral visitors. Galen has found that when looting ants crawl inside skypilot blossoms for nectar, they rip the flower's style out of the way, haul it upward, and heave it, like trash, past the flower's mouth. Afterward, the damaged flower cannot set seed. Reporting last year in Evolution, Galen demonstrated that ants favor flowers with easy access via a flared, short corolla. Alpine skypilot populations in ant-damaged areas, she predicts, will likely evolve a more narrow, tubular neck to welcome pollinating bees but deter ants. “Ants could have a significant impact on the evolution of the flower's shape,” Galen says.

    Shaped by thieves?

    Rocky Mountain field experiments find that nectar-thieving ants might play a part in shaping the alpine skypilot wildflower.


    In addition to ants, flowers face a traveling mob of other predators, including slugs, aphids, thrips, and caterpillars. Researchers want to know how these actors affect floral design. In work to be published in the journal Ecology, Strauss and her colleagues have found that both pollinators and herbivores tend to prefer wild radish plants bearing yellow or white flowers rather than plants with pink or bronze blossoms. How do the selective pressures of pollinator and predator play out?

    “We're not always good at identifying the important selective agents for a floral trait,” Strauss says. “Pollinators seemed to be the obvious choice for a long time—and clearly, they are important. However, we're finding there are a lot of other forces we've been less likely to look at.”

    But traditionalists aren't prepared to surrender the pollinators' primacy. “One could do the odd study and show an effect from predators in one species,” says Spencer Barrett, an evolutionary biologist at the University of Toronto. “But I'm not sure that one or even a few studies are going to overturn the intuitively reasonable hypothesis that flowers are so varied in shape and size because they have been modeled by natural selection by pollinators.”

    Douglas Schemske, an evolutionary biologist at Michigan State University in East Lansing, agrees. “We really don't have efficient means for measuring selection in all but the strongest cases,” says Schemske. “If somebody says they didn't find evidence of pollinator selection, is it really missing, or, say, is their sample size not big enough?”

    What's more, Schemske contends, even if a study fails to find pollinator selection for a floral trait today, that selection still could have happened in the past. That's a difficult argument to counter, notes Galen: “You could always say something happened in the past, and we just can't measure it.”

    But revisionists are acquiring the tools needed to probe historic influences as well. Reporting this summer in the Journal of Evolutionary Biology, W. Scott Armbruster of the Norwegian University of Science and Technology in Trondheim and the University of Alaska, Fairbanks, used comparative phylogenetics to see whether past pollinators—or unrelated developmental changes—were more likely to have inspired diverse flower colors in a vine, Dalechampia, and in maple trees.

    A colorful moment.

    A new phylogenetic study suggests that Dalechampia evolved new colors as a biochemical defense, not to lure pollinators.


    Dalechampia is a tender vine prized for its colorful floral bracts, or petal-like leaves. Armbruster retraced the evolutionary origins of four color types in various Dalechampia species, along with the emergence of the vine's major pollinators. In this study, widely praised as innovative, Armbruster didn't find a tight evolutionary link between pollinators and color.

    Instead, he concluded that new Dalechampia bract colors emerged at the same time that the plants acquired the purple-red pigment anthocyanin in unrelated vegetative organs, probably as a biochemical defense against harmful radiation, drought, herbivores, or pathogens. In other words, the bract colors likely evolved simply as a byproduct of the protective vegetative pigments—not in response to the pressure of major pollinators, which remained unchanged at that time in the historical record.

    “I'm interested in evolution via natural selection as much as the next person,” says Armbruster. “But my feeling is that we have to work our way through a series of simpler explanations before we invoke adaptation for every floral trait.” No one knows, he adds, just how often such developmental or genetic events, versus pollinator selection, have pushed flowers to evolve a given design. “Maybe this happens rarely, or maybe it happens often,” Armbruster says. “We don't have enough data to know the balance of the processes.”

    But he hopes that will change. As more scientists bring sophisticated tools and questions to the study of floral evolution, Armbruster adds, the field will better reflect reality. “A plant is out there experiencing all these forces simultaneously,” he says. “It's only biologists who look at them one at a time.”


    Europe's Black Hole Hunter Is Ready to Fly

    1. Govert Schilling*
    1. Govert Schilling is an astronomy writer in Utrecht, the Netherlands.

    The most turbulent and cataclysmic events of the universe should soon give up their high-energy secrets to Europe's Integral observatory

    UTRECHT, THE NETHERLANDS—Supernovas, gamma ray bursts, black holes, neutron stars, active galactic nuclei, and sites of massive matter-antimatter annihilation: They're among the universe's most violent scenes of mayhem. Astronomers are falling all over themselves to get a good look at these unsavory neighborhoods, hoping for fresh insights into everything from the origin of the heavy elements to the death throes of massive stars.

    Later this month, if all goes according to plan, astronomers should have an orbiting observatory in place that will provide the best views yet: Europe's International Gamma-Ray Astrophysics Laboratory, or Integral. It will be “the first spacecraft to make detailed gamma ray images of the sky,” says Neil Gehrels of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is U.S. mission scientist for Integral. Anticipation is running so high that the first year of observing time is already oversubscribed—by a factor of 20.

    The $600 million Integral, 9 years in the making, carries the heaviest set of instruments ever lofted by the European Space Agency (ESA). Following its planned launch by a Russian Proton rocket, slated for 17 October, Integral will carry on where NASA's Compton Gamma Ray Observatory left off. Compton, which ended its life in a fiery reentry 2 years ago, carried out sky surveys at all kinds of gamma ray energies. Integral, in contrast, will focus on low- and midenergy gamma rays with much higher sensitivity, more acute vision (comparable to the human eye's), and better spectroscopic precision.

    Gamma rays are the most energetic photons in the universe—about a million times more energetic than visible light. They emerge only from the most extreme environments. Despite their power, gamma rays are rare and hard to catch: They don't penetrate Earth's atmosphere and are impossible to focus with lenses or mirrors. Instead, gamma ray astronomers must rely on elaborate space-based pinhole cameras known as coded mask apertures and sensitive semiconductor detectors that must be cooled to low temperatures and heavily shielded from background radiation.

    Integral carries four wide-angle instruments: a gamma ray camera, a gamma ray spectrometer, an x-ray camera, and an optical telescope. Project manager Kai Clausen of the European Space and Technology Centre (ESTEC) in Noordwijk, the Netherlands, calls the technology of the gamma ray instruments “mind-boggling.” For instance, the French-Italian camera contains more than 20,000 individual cadmium telluride and cesium iodide detectors, each measuring a few millimeters across and outfitted with its own set of miniature amplifiers. The French-German spectrometer is 100 times as sensitive as similar instruments flown in the past and has 19 semiconductor detectors of ultrapure germanium. To protect all these delicate instruments, Integral must lug around massive detector shields, made of bismuth germanate oxide crystals.

    In all, Integral measures 5 meters high and 3.7 meters in diameter and weighs 4.1 tons. Like ESA's XMM-Newton x-ray satellite, launched in 1999, Integral will be placed in a very elongated orbit, spending 90% of its time well outside the noisy environment of Earth's radiation belts. During its first year in orbit, the researchers who built the instruments will get 35% of Integral's observing time; 26% of the remainder is earmarked for Russian astronomers, in return for the free launch Russia is providing.

    Much of the time, Integral's instruments will be pointed in the general direction of the center of the Milky Way, where more than half of the galaxy's transient high-energy sources are located—predominantly neutron stars and black holes in binary systems. “Integral is a true black hole hunter,” says acting project scientist Arvind Parmar of ESTEC. “Every Monday morning, it will scan the galactic plane, looking for new sources.” As soon as a new burst is detected, a dedicated follow-up campaign will commence. The observations will shed light on the way these bizarre objects influence their immediate environment.

    Thanks to its high spectral resolution, Integral will also be able to look for the fingerprint of radioactive atoms that are produced in the aftermath of supernova blasts. “By precisely determining the amount of decaying elements like titanium and cobalt, we will learn more about the way heavy elements are synthesized during supernovas,” says Wim Hermsen, an Integral mission scientist at the Space Research Organization Netherlands in Utrecht. He adds that Integral will reveal the true supernova rate in our galaxy, as it will detect all young supernova remnants in the Milky Way that have escaped detection at other wavelengths.

    Farther from home, the new observatory will focus on the supermassive black holes in the cores of active galaxies and their relativistic jets of ejected material, shed light on the origin of ultrahigh-energy cosmic rays, and uncover major matter-antimatter annihilation sites, such as the one found near the huge black hole at the center of the Milky Way. Also, scientists expect a yearly catch of about 20 gamma ray bursts: titanic explosions of giant stars that probably signal the birth of black holes. Because Integral's instruments always look in the same direction, new bursts will be observed simultaneously at optical, x-ray, and gamma ray wavelengths.

    Although Integral ignores the highest energy gamma rays, that gap will soon be filled by the Gamma-ray Large Area Space Telescope, which NASA will launch 4 years from now. ESA plans to operate Integral for at least 2 years, but it is likely to extend the mission through 2007, so the two observatories might operate in parallel for at least a year. “Especially for the study of active galactic nuclei, this would be a very nice capability,” says Gehrels.

  14. Creatures of Our Own Making

    1. Stephen Budiansky*
    1. Stephen Budiansky is a correspondent for The Atlantic Monthly. His latest book is The Character of Cats (Viking).

    After millions of years of coexistence, the lives of humans and mosquitoes have become intricately intertwined. The mosquito's ability to exploit almost any type of water—natural ponds and marshes or human creations such as irrigation ditches and used tires—is testimony to its evolutionary ingenuity

    To say that the malaria-carrying mosquito Anopheles gambiae is well adapted to its role as a human parasite is like saying that Pavarotti is a pretty good singer.


    An. gambiae, native to tropical Africa, is just one of about 60 anopheline mosquitoes throughout the world that can transmit human malaria. But its unrelenting focus on human ways has made it a prodigy as a disease vector. An. gambiae typically breed in temporary, sunlit puddles and pools of a kind found in particular near human habitations and usually directly associated with humans' agricultural modification of the landscape: the water that collects in irrigation ditches and even the small puddles created where livestock have depressed the soil with their hooves. Adult An. gambiae mosquitoes are commonly found sheltering in huts during the heat of the day. At night they emerge from their resting spots and, lured by the odor of human feet and other scents (see p. 90), home in on their preferred prey.

    Blood feast.

    Using two stylets, an Anopheles gambiae slices through human flesh in search of a meal.


    The exquisite apparatus that the female employs to penetrate the skin of its victim is less like a simple needle than one of the “complex devices surgeons snake through a body to perform remote-control surgery,” observes Andrew Spielman of Harvard School of Public Health in Boston, a leading mosquito researcher. At the end of the mosquito's slender proboscis are two pairs of cutting stylets that slide against one another to slice through the skin—“like a pair of electric carving knives,” Spielman writes in a mesmerizingly gory description of mosquitoes at work in his recent book, Mosquito: A Natural History of Our Most Persistent and Deadly Foe.

    Once through the skin, the mosquito's proboscis begins probing for a tiny blood vessel. If it does not strike one on the first try, the mosquito will pull back slightly and try again at another angle through the same hole in the skin. Inside the proboscis are two hollow tubes, one that injects saliva into the microscopic wound and one that withdraws blood. The mosquito's saliva includes a combination of antihemostatic and anti- inflammatory enzymes that disrupt the clotting process and inhibit the pain reaction—the better not to get swatted—during the minute and a half or so while the insect is feeding. (Only later does the leftover saliva provoke an allergic reaction that often leaves the characteristic raised welt of the mosquito bite.) Spielman believes that the suite of enzymes produced by particular species of mosquitoes is closely tailored to the biochemistry of its chosen hosts. An. gambiae thus probably produces enzymes that work best against the clotting and inflammatory biochemical pathways of its preferred target: humans.

    Nonnegotiable demand.

    Mosquitoes must have water to lay their eggs, but various species have adapted to whatever sources are available, be they natural ponds, used tires, or water barrels. Lighted gasoline (right) can kill mosquito larvae.


    Although humans have been around for only a couple of million years, mosquitoes have always been with us—“us” being that fraternity of mammals, birds, reptiles, and no doubt dinosaurs, bound together by common victimhood at the hands, or rather the proboscises, of the members of the family Culicidae. The word mosquito comes from the Spanish or Portuguese meaning “little fly,” which is both apt description and good taxonomy. Mosquitoes are members of the order Diptera, the earliest “true” flies. Nora Besansky of the University of Notre Dame in Indiana, an expert on mosquito evolution, estimates that the divergence between the mosquito lineage and the “higher” flies such as Drosophila took place about 250 million years ago. The oldest known mosquito fossil, preserved in Canadian amber, dates from about 76 million to 79 million years ago; and, notes entomologist Thomas Zavortink of the University of California, Davis, an expert on mosquito taxonomy, “it's a perfectly good mosquito; it's not something that looks halfway between a mosquito and something else.” Zavortink concludes: “When you put it all together, I'd say mosquitoes have to have evolved 160 [million] to 205 million years ago.”

    Over the eons since, mosquitoes have charted an impressive record of adaptation, diversification, and spread. The 5-cm-thick Catalog of the Mosquitoes of the World lists a couple of thousand species; adjusting for new discoveries, the total comes to about 3500 known and identified species throughout the world. Zavortink has estimated, however, that “we probably know only a quarter of the species” of mosquitoes actually in existence. (He hastens to add, “Maybe I'm wrong and it's half.” Either way, that's a lot of mosquitoes.)

    Although people commonly think of mosquitoes as being particularly associated with swamps or steaming tropical jungles, they are found in practically every habitat and climate zone on Earth, from the equator to the Arctic. The Arctic, in fact, is home to some of the most suffocating mosquito populations on the planet, albeit only for a few brief weeks of the year when the surface waters of the tundra melt. Dead caribou have been found completely exsanguinated, their blood literally sucked dry by swarms of ravenous mosquitoes that beset the still-warm corpses. The one nonnegotiable demand in the mosquito life cycle is that all mosquito larvae need to live in water, where they feed upon aquatic microorganisms as they develop. But the ability of the mosquito family to exploit suitable bodies of water in climates ranging from deserts to mountaintops (mosquitoes have been found at an elevation of 2400 meters in the Himalayas) is a staggering testimony to evolutionary ingenuity. The water can be fresh, salt, brackish, or sewage; it can be found in ponds, lakes, streams, bogs, marshes, ditches, puddles, barrels, birdbaths, tree holes, or even the leaves of the pitcher plant. Dozens or even hundreds of different mosquito species may exist in the same geographical area, each exploiting a slightly different niche among the panoply of damp places.

    Coexisting mosquito species have also found ways to spread out ecologically within an environment: by concentrating on different hosts; by being generalists or specialists; by adopting different search and attack strategies; and by being active at different times of day. As a general rule, the mosquito species that are active during the day tend to use visual cues rather than odor to find their victims. They cue in on motion and tend to be fairly nonselective in their targets. (Odors are very specific to individual species, whereas a lot of animals move.) The infamous New Jersey mosquito, Ochlerotatus sollicitans, attacks like a Stuka dive-bomber from directly above, usually biting the head or upper body of its victim, and even chases victims who try to run away. Other common North American mosquitoes occupy distinct niches. The common house mosquito, Culex pipiens, implicated recently as a major vector of West Nile virus in the United States, feeds at night and strikes birds, livestock, and people; it appears to be attracted generally by heat and carbon dioxide. The dengue and yellow-fever mosquito Aedes aegypti feeds in morning and late afternoon and is “semidomesticated” in its habits, breeding almost exclusively in water that collects in small artificial containers around human habitations and preferring the blood of humans to that of other animals. The swamp mosquito Culiseta melanura—the major carrier of the deadly viral disease eastern equine encephalitis—breeds in subterranean pockets of water that form under tree roots and feeds almost exclusively on birds. A few mosquito species have adapted to the competition by eschewing blood altogether; Toxorhynchites mosquitoes live off nectar.


    The unifying theme in this diversity, says Spielman, is that “mosquitoes are well adapted to a very unstable, transient environment. They're the first organism in and the first out of a newly created body of water.” Not only do transient water bodies—those that form in tree cavities or seasonal waterways, for instance—provide an opportunity for breeding that might not otherwise exist in a dry region, but even in moist and temperate areas they offer the further advantage of helping mosquitoes evade predators. Mosquito eggs and larvae are extremely vulnerable to predation. But in small, temporary puddles or seasonally filled ditches, they can finish their 1- to 2-week development into pupae and adults before other carnivorous insects appear on the scene. Small, transient pools are also free of such formidable predators as fish. Some mosquitoes, notably the Aedes species, lay their eggs on the moist edge of a receding, seasonal stream or pool or a partially filled artificial container. The eggs stay moist for a day or two while the embryo develops, but then further development is placed on hold as the water evaporates. When rains later raise the water level, the resulting reduction in oxygen tension immediately triggers the eggs to hatch—within literally half a minute.

    The other way mosquitoes cope with predators is through the strength that comes in numbers, and that's where blood-feeding comes in. In some aquatic insect species, such as mayflies, adults emerge from pupation lacking even functional mouthparts: The adults breed and die quickly, without ever feeding. But to acquire the nutrients needed to produce the hundreds of eggs that a single female mosquito can lay, some concentrated form of energy is required. Even in blood-feeding species of mosquito, it is only the female that does so. The few micrograms of blood she sucks from her host represent three times her own weight and constitute a nutrient-rich bonanza that is scarcely available in such concentrated form elsewhere in nature. In general, notes Zavortink, the mosquito species that do not feed on blood occupy a habitat where the larvae live in nutrient-rich environments and so can accumulate the needed supply of egg-laying nutrients before reaching adulthood. Further proof of the connection between blood and abundant reproduction is found among the variant subpopulations of C. pipiens: Spielman found that some C. pipiens subpopulations do not feed on blood and lay about 60 to 80 eggs only once in their lifetime. Other variants feed on blood repeatedly and produce as many as 400 eggs per blood meal. This “adaptive polymorphism,” as Spielman describes it, enables the species “to thrive whether or not there is a host available.”

    The role that human behavior and modification of the environment have played in the evolution of the mosquito—and of the many diseases that mosquitoes can transmit to humans, among them yellow fever, malaria, dengue, West Nile virus, encephalitis, and elephantiasis—is extraordinarily complex. In recent centuries human travel, trade, and development have repeatedly introduced species to new habitats and, for that matter, created entirely new habitats. Ae. aegypti was brought to the New World in the 17th century, along with yellow fever, probably in the water casks of slave ships that sailed from Africa. In the 1970s, the Asian tiger mosquito Ae. albopictus was inadvertently carried to Texas amid shipments of used tires. Ae. albopictus is a tree-hole-breeding species, and the water that accumulates in a dismounted tire offers a perfect artificial counterpart to its natural habitat. The tiger mosquito does not appear to be a significant disease vector in North America, but it is notoriously aggressive, attacking in daylight.

    On a local scale, recent human modification of the environment may also have dramatic consequences for the interaction of human and mosquito. Having been introduced into South American rainforests, Ae. aegypti began to occupy its natural habitat of tree holes, high in the forest canopy. Spielman says one can walk through such rainforests for kilometer upon kilometer without encountering mosquitoes at all. But that is only as long as the forest remains intact. When trees are felled, the mosquitoes are abruptly brought to the forest floor—and into contact with people.

    The few decades that Ae. albopictus has been breeding in used automobile tires, or even the few centuries that Ae. aegypti has been breeding in water barrels or other such niches inadvertently created by modern commerce and land-use patterns, are too short to have had a major impact on mosquito evolution. But intriguing genetic evidence points to a significant human role in the recent evolution of the African malaria vector An. gambiae and other closely related species. Indeed, the potent niche that human beings and human modifications of the landscape represent seems to have driven a burst of speciation that, Besansky and some other researchers believe, is continuing even now—and that genetic analyses on the molecular level are capturing as it unfolds (see p. 87).

    In the 1960s entomologists realized that what had been believed to be the single species An. gambiae is actually a complex of seven closely related “cryptic” species. These seven species cannot be distinguished “by eyeballing them,” Besansky notes, but significant differences appear in their DNA sequences. There is a high degree of breeding isolation among these molecularly distinct species. There is also a high degree of feeding specialization: Among the seven are some (such as An. gambiae “proper”) that concentrate almost exclusively on humans and others (such as An. quadriannulatus) that feed almost exclusively on animals.

    Similarly, another major African malaria vector, An. funestus, is part of a subgroup of four very closely related sister species. An. funestus alone among them specializes in human hosts; it is found almost exclusively resting inside human dwellings and feeding on human blood. Indeed, most of the world's 60 anopheline mosquitoes that are human malaria vectors (out of the 500 or so Anopheles mosquito species in all) belong to similar complexes or groups of extremely closely related species.

    Mitochondrial DNA analysis suggests that An. gambiae and An. funestus diverged about 4 million to 6 million years ago, which, Besansky notes, is approximately when human and chimpanzee also diverged. “Until quite recently, humans haven't been around on the planet in sufficient density that a mosquito would choose to specialize to such an extent” as An. gambiae and An. funestus do, she observes. “So you can at least speculate that it was the rise of human density and the accompanying environmental modification that triggered these bursts of diversification throughout the anopheline species.”

    Molecular analysis of different populations within An. gambiae proper suggests that further speciation is occurring even now. Two molecular forms have been identified within An. gambiae proper, the M and S forms (see Coluzzi Report at and Della Torre Viewpoint on p. 115). Analysis of the sperm found in impregnated females shows that only about 1% of matings occur between members of the two different forms. Moreover, striking behavioral differences exist between the two populations. The S form, which is found throughout tropical Africa, breeds in rain-dependent temporary puddles. The M form, which is found only in West Africa, breeds preferentially in humanmade environments such as irrigation ditches. These ditches typically remain filled with water for much longer periods of the year than do puddles. In other words, the M form appears to be an “incipient species that is taking advantage of habitats man has created,” Besansky says. Its emergence has had the effect of “extending the reach” of An. gambiae—and of the malaria parasite it carries—“both physically and temporally,” Besansky says: An. gambiae is penetrating into regions that were previously too dry to support it at all, and it is extending the seasons of the year during which it can breed, even in areas where it was previously found.

    The fine-tuned adaptation of anopheline mosquito species such as An. gambiae and An. funestus to preying upon humans seems to clearly explain why these are such important vectors of human malaria. In the laboratory, all of the seven species that make up the An. gambiae complex can be infected with malaria. Yet in the wild, only those species that attack humans carry the parasite. The reason is largely a matter of mathematics. To successfully transmit the disease from one human to another, a mosquito has to have a high probability of biting an infected human being (“focused feeding”) and also has to live long enough to bite another uninfected human being after the parasite has undergone the necessary stage of development within the mosquito's gut. A mosquito that “wastes” some of its bites on nonhumans will be a much less efficient vector of a human pathogen.

    The mathematics of vector-borne disease transmission produces some fascinating and not always intuitive results. The population density of a vector is actually far less significant in determining how efficiently it spreads disease than are the factors of focused feeding and longevity. Beginning a century ago, the United States began an antimosquito war that continues to this day; every state and many counties and districts have “mosquito control” authorities that spray insecticides, drain ditches and swamps, and even distribute mosquito-eating fish to pond owners. Their work has been remarkably effective in reducing populations of nuisance mosquitoes. But the elimination of once-endemic diseases such as malaria, yellow fever, and denguelike fevers from North America occurred largely as a result of changes in human behavior that reduced human contact with mosquitoes, not through specific control or elimination of the disease vectors themselves. Indeed, temperate North America and Europe are still home to significant populations of perfectly efficient malaria, dengue, and yellow-fever vectors. Paul Reiter, a medical entomologist at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, notes that “we associate malaria with the tropics only because we've forgotten—because we've relegated malaria to the tropics.”

    Reiter, who has extensively researched the history of vector-borne diseases—he is also CDC's point man on the West Nile outbreak—notes that malaria was regularly found as far north as Canada and Scandinavia in the 19th century. It was endemic in England even during the unusually cold weather of the “Little Ice Age” of the 17th century. Severe outbreaks of yellow fever occurred in Philadelphia repeatedly in the 17th and 18th centuries; in the 1793 outbreak, 5000 people died—a tenth of the city's population. Philadelphia was also the site of the first recorded outbreak of denguelike fever in America, in 1780. The United States was declared malaria-free only in 1954; Holland achieved that status only in 1970.

    Yet the incidence of malaria began to decline dramatically in the industrializing nations toward the end of the 19th century, well before mosquito-control programs began—indeed, before mosquitoes were recognized as the carriers of the disease. Better housing and sanitation played a significant part, but nothing did as much as the advent of one remarkably simple device in the early 20th century: the window screen. Breaking the chain of transmission was the crucial factor. If each infected person transmitted the disease on average to fewer than one other person, the epidemic would be broken and the population of the disease-causing organisms would not be able to sustain itself. That is what ultimately happened. As Spielman notes, the mosquito survived, but the parasite it transmitted did not.

    Reiter's studies of history and his current-day field research on mosquitoes have convinced him that recent dire warnings of a resurgence of vector-borne disease due to global warming have at best a dubious basis in scientific fact. “Obviously, climate and weather are important,” he says. But countless mosquito species, including many perfectly efficient disease vectors, are capable of surviving cold winters, either by hibernating in basements or other sheltered areas or in the form of impervious eggs. “In the end, human behavior and the economic conditions of people are probably the most important factors” in determining the distribution of vector-borne diseases, he argues. Reiter points to the striking example of dengue along the Rio Grande: From 1980 to 1999, there were 64 cases in Texas versus 62,514 in the three Mexican states on the other side of the river. Yet the population of dengue-carrying Ae. aegypti is actually greater on the U.S. side. The crucial difference is that in Mexican towns and cities, window screens are rare and people are constantly out on the streets exposed to the disease carriers. But “on the streets in Texas, you're lucky if you see someone dashing between their air-conditioned vehicle and their air-conditioned house,” as Reiter puts it.

    The close triangular association among humans, mosquito species such as An. gambiae and Ae. aegypti, and the diseases they carry has led to some speculation that the pathogens might be influencing the evolution of mosquitoes in ways that make them more effective disease carriers and vectors. But most experts believe that is not the case; rather, the parasites are merely opportunistic piggybackers that are exploiting the preexisting close relationship between mosquitoes and humans. Spielman points out, too, that at least some of the mosquito-borne pathogens are harmful not only to the human or animal host but to the mosquito vector as well, notably the various filarial worms (responsible for elephantiasis in humans and heartworm in dogs), whose larvae, to avoid being harmed by the mosquito's digestive tract, burrow out of the gut and into the wing muscles, where they develop. (They subsequently burrow their way to the mosquito's mouthparts, breaking out as it feeds and so gaining entry to the host's bloodstream.) Thus, if anything, there should be a selective pressure that tends toward mosquitoes' resisting the role of disease carrier.

    Spielman speculates, however, that in a paradoxical way, humans—the ultimate victims of diseases such as malaria—might themselves create selective pressures that help keep the rates of malaria infection and transmission high. Spielman notes that where malaria is endemic, the resident population tends to have developed immunity to the disease. Although infection rates are high, incidence of disease symptoms is low; even infants are protected to a significant degree by passive immunity acquired from antibodies in their mothers' milk. An invading enemy, however, would not only be quite likely to be infected but also be quite likely to succumb to the disease. “These ‘diseases of the enemy’ like dengue and malaria protect the residents of stably infected sites,” Spielman argues. “A lot of the things that mosquitoes transmit are nasty, and they're that way on purpose—to keep visitors away.”

    So, as with many aspects of this close and troubling relationship between humans and mosquitoes, the fault may lie less with them than with us.

  15. Mosquitoes and Disease

    1. Leslie Roberts

    This map shows the most important malaria vectors in areas where the disease is endemic, as well as the distribution of major mosquito-borne diseases including dengue, lymphatic filariasis, yellow fever, and Japanese encephalitis.

  16. In Pursuit of a Killer

    1. Gretchen Vogel

    Armed with microscopes, tweezers, and modified Shop-Vacs, researchers in West Africa are hunting malaria mosquitoes

    OUAGADOUGOU, BURKINA FASO—A basic rule of military intelligence is to know the enemy inside and out. Learn his habits, strengths, and weaknesses. The same holds true in the fights against malaria, dengue fever, filariasis, and West Nile virus. If public health experts are to have a chance at controlling these diseases, they need to understand exactly how the maladies' main ally—the mosquito—operates.

    To deploy weapons effectively, from low-tech bed nets to high-tech transgenic mosquitoes, researchers have to understand the battlefield. They must know not only how many of these pests plague a community, but also which specific genetic types are prevalent, where they gather at feeding time, where their resting places are, and where they lay the eggs that produce the next generation. “Where malaria has been controlled anywhere in the world, it has been done by controlling mosquitoes, not through vaccines or genetics or anything fancy,” says entomologist Robert Gwadz of the laboratory of parasitic diseases at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland.

    Despite having research budgets that are a tiny fraction of those spent to sequence the mosquito genome (see p. 92), several teams of entomologists are in active pursuit of the world's deadliest animal. They are beginning to characterize a dizzying array of genetic subtypes, learning what makes them dangerous—and vulnerable.

    Because of its location between rainforest and dry sahel, Burkina Faso has perhaps one of the heaviest mosquito burdens in Africa. Indeed, malaria is so thoroughly entrenched here that public health leaders in the 1960s quietly left it and its neighbors out of so-called world eradication strategies. Even eliminating nine out of 10 of the insects in some parts of the country would make little dent in disease prevalence, says Carlo Costantini, an entomologist at the University of Rome who has worked in the region since 1991. In the capital city of Ouagadougou, along streets lined with vendors selling mangoes, pottery, car parts, and cell phone cards, one of the most common billboards is for a popular brand of insecticide. A spray can looms victorious over a dead mosquito, legs in the air. “Creatures of the good Lord?” the caption reads. “Too bad!”


    Burkina Faso suffers from one of the heaviest mosquito burdens in Africa.


    Not far from one such billboard, and just off a dusty main street clogged with bicycles, mopeds, and vintage Renault taxis, is the National Center for Research and Training on Malaria (CNRFP). There, funded by the National Ministry of Health and grants from the Italian, Dutch, and Swiss governments, a team of eight researchers and technicians is sorting out the mosquito tangle. The group is led by N'Falé Sagnon, who grew up in Banfora in southwest Burkina Faso. Sagnon became interested in entomology as a university student in Algeria when he joined a project studying the black fly, which transmits river blindness. In 1999, he earned his Ph.D. at the University of Rome working with entomologist Mario Coluzzi and Costantini; he returned to the center in Burkina Faso the next year to build a team of entomologists.

    Captured quarry.

    As part of a mosquito census, researchers collect mosquitoes from different sites in the village.

    Sagnon's team, working with Edith Ilboudo-Sanogo of CNRFP, Costantini, and Nora Besansky of the University of Notre Dame in Indiana, is trying to determine the behavior and genetics of the region's malaria-transmitting mosquitoes. Burkina Faso's bug demographics are some of the most complex in Africa, Costantini says. Local mosquitoes have adapted so well to the seasonal variations that in many areas, instead of appearing just in the rainy season, they are year-round pests. Culex species are a nuisance but pose little threat. Several others are killers: Aedes aegypti, which can transmit yellow fever and dengue, and the malaria vectors Anopheles gambiae and An. funestus. Two genetically distinct forms of An. gambiae “proper” are present. (An. gambiae proper is one of the seven sister species researchers identified in the 1960s that make up the An. gambiae complex.) These are the Mopti (M) form, which is especially adept at exploiting human-created water sources such as irrigation ponds, and the Savanna (S) form, which takes advantage of rain-triggered water sources such as puddles (see p. 80). An. funestus, the second malaria vector in Burkina Faso, might also be a complex of several distinct genetic types, recent research at the center suggests.

    Hoping to target the most dangerous malaria transmitters, the team is sorting out behavioral differences among the various populations. Although they look the same, the different forms have distinct preferences in where they lay their eggs as well as their relative taste for human or animal blood. And the competition between them—for water in which to lay their eggs, shady resting places, or blood meals—means that some vector-control measures that hit one form especially hard might give its competitor an unintentional boost, notes Costantini. “The more you know about your vector, the better you will predict how it will respond” to different control strategies, he says.

    Where the streets have no name

    Both An. funestus and the two forms of An. gambiae plague Goundri, half an hour northeast of Ouagadougou. An uninitiated driver could easily miss the turnoff for the village: a gravel slope off the paved road marked with a hand-lettered wooden sign. The rutted road winds through fields of millet, maize, and peanuts. Scattered over 2 square kilometers are more than 500 mud-brick and thatch-roof huts clustered into about 100 compounds. Goundri looks like thousands of other villages in central Burkina Faso, with one exception: Every structure, from the concrete-brick mosque to the simplest grain storage hut, has a large blue number spray-painted on its side—especially striking in a region where street numbers are rare. The numbers are courtesy of geographers from CNRFP, who last year used geographic information systems (GIS) data to map the precise location of every building. The GIS map is proving invaluable as the researchers collect mosquitoes from various locations and attempt to learn whether different genetic types have special preferences for residing indoors or outdoors, near water or near animal enclosures.

    The hunt.

    Researchers use a hand-held vacuum (top) to capture dozens of mosquitoes in their daytime resting places (bottom).


    The tools for a mosquito census are fairly simple: a few long-handled dippers for collecting eggs and larvae, a type of modified Shop-Vac for capturing adults, paper cups, and a cooler filled with ice. Inside huts, team members search the walls and any protected corners for quarry, which are plentiful. The folds of hanging clothes swarm with mosquitoes when a visitor brushes up against them. The Shop-Vac—a hand-held vacuum fitted with a long nozzle and a net- covered cup instead of a dust bag—whirs as the researcher collects a dozen mosquitoes in a single pass. The paper cups filled with whining bloodsuckers are labeled with the collection time and place and then transferred to the cooler. In 10 minutes, the disarmingly fragile insects are dead.

    Back in the lab, team members dissect the mosquitoes. Nothing from the tiny bodies goes to waste. Tests on the salivary glands determine whether the insects were carrying plasmodia, the parasites that cause malaria. The gut is used to determine whether the last blood meal was from a human, cow, goat, or other animal. Polymerase chain reaction (PCR) analysis on the rest of the body can determine whether the insects are M or S forms.

    Over the last decade, mosquito censuses in Goundri and a half-dozen similar villages around the country have revealed a consistent pattern: At the beginning of the rainy season in July, the An. gambiae M form is most prominent—not surprising, perhaps, for a subtype that prefers relatively permanent bodies of water. A few months later, as the constant rains raise the water table and increase the number of temporary puddles, the S form's population increases. As the rainy season ends in October, An. funestus begins to appear in irrigated rice fields and artificial reservoirs, transmitting malaria even through the hot, dry days of April.

    Tiny microbiologists

    The availability of open water is what distinguishes those periods, and the researchers suspect that differences in water use are driving the genetic subgroups apart—a step toward separating into distinct species. “The larval stage is where competition [between mosquitoes] is felt most keenly” and therefore is a focus for speciation, says Notre Dame's Besansky.

    The eggs' fate might depend on whether they are laid in a temporary or permanent pool, but how does the female mosquito distinguish between the two? The Ouagadougou team has found some early evidence that bacterial signals might be key. Wamdaogo Moussa Guelbeogo, a Ph.D. student at the University of Ouagadougou, collected water samples from long- and short-lived pools and cultured the bacteria in each. He and his colleagues identified 12 strains of bacteria, several of which were exclusive to either longer term or ephemeral pools.

    To test female An. gambiae, he placed a single mosquito that was ready to lay her 300 or so eggs in a net cage containing shallow bowls of water seeded with bacteria—those typical of either temporary or more permanent ponds. When given a choice between the bacterial cocktail from temporary or permanent pools, the M-form females, he found, preferred to lay their eggs in the permanent one. S-form mosquitoes, on the other hand, preferred the temporary-pool bacteria. And when faced with only one option, the M-form females exhibited distinctive behavior. When they sensed bacteria from a permanent water source, they were more likely to lay all their eggs at once. But when they were given water laced with bacteria from a shallow pool, the insects tended to lay their eggs in several batches—perhaps ensuring that even if one water source dried up quickly, another might last long enough for the eggs to develop fully. “The mosquitoes are better at identifying bacteria than most microbiologists,” says Coluzzi.

    In the short term, such knowledge might be useful for building effective mosquito traps—both for research and for vector control, says Guelbeogo (see p. 90). In the long term, he says, researchers might be able to develop a genetically altered strain of bacteria that could both attract egg-laying females and produce a toxin that would kill developing larvae. The idea is futuristic, Costantini admits, but he points out that Bacillus thuringiensis israelensis, a bacterium that releases toxins that are safe for humans but lethal to mosquitoes, is already in use as an antilarval pesticide.

    Cellular bar codes

    This year, CNRFP entomologists are targeting the more elusive An. funestus. Relatively little is known about the species, first described at the beginning of the 20th century, except that it is not particularly research-friendly. It grows poorly in captivity, rarely reproducing for more than four generations. Its larvae are extremely difficult to capture: Females prefer to lay their eggs in water with plenty of vegetation to provide hiding places, and as soon as a shadow passes over their pool, the larvae dive for the bottom and remain hidden for up to 30 minutes.

    Permanent accommodations.

    Lakes such as this one outside Ouagadougou provide year-round habitats for mosquito larvae, one reason why the mosquito burden is so high.


    Costantini and Sagnon have preliminary evidence that this species, too, is really two distinct genetic subtypes, which they have dubbed Folonzo and Kiribina for two of the villages where the studies were done. Like the An. gambiae subtypes, the two potential subspecies look exactly the same even to an expert. And researchers do not yet have PCR-based markers that can distinguish between the two, as they do for the An. gambiae subtypes. Experts can identify different types of An. funestus by examining light and dark patterns in oversized chromosomes, which under the microscope resemble a sort of cellular bar code. Like M and S, Folonzo and Kiribina are characterized by specific chromosomal inversions: regions where the band pattern is flipped.

    In mosquitoes, these polytene chromosomes appear only in certain cells in the maturing ovary. To isolate them, researchers must capture “semigravid” females: insects that have digested half of their blood meal, usually about 18 hours after feeding. Males—or females that have not recently fed—are useless for genetic typing.

    The team hopes that will soon change. Besansky and her colleagues in Indiana are working to identify DNA markers that correspond to the chromosomal inversions. If they succeed, researchers will be able to identify all collected mosquitoes by genetic type, not just the recently fed females. That will make it possible for the first time to analyze patterns of distribution of the two genetic types throughout their life cycle. Unfortunately, An. gambiae and An. funestus have diverged enough through evolution that this week's completed An. gambiae genome is unlikely to help the An. funestus effort, Besansky says.

    The early chromosome-based evidence suggests that gene flow is restricted between the Kiribina and Folonzo types—even among An. funestus populations living in the same village or the same hut. “We're not saying they're different species, but the chromosomal markers we're using are not mixing the way they would if they were completely interbreeding,” Besansky says. And Sagnon and Guelbeogo's latest work suggests that the Folonzo type might be more involved in malaria transmission. Those mosquitoes are more likely than their Kiribina cousins to have bitten humans and to be found indoors—a ripe target, perhaps, for public health's best weapons.

  17. What Mosquitoes Want: Secrets of Host Attraction

    1. Martin Enserink

    Why do mosquitoes feast on some people and leave others alone? Researchers are trying to find out, hoping it will help them design the perfect mosquito trap

    Life isn't fair. Whereas some people never seem to get bitten by mosquitoes—and often don't even seem to notice the critters—others spend their evenings frantically swatting them, usually to no avail. If you're in the latter category, you've probably wondered: Why me? Is it thin skin? My gorgeous body odor? Sumptuous blood vessels begging to be punctured? Or is it all between the ears, as some people say, and you simply fuss and fret more about mosquito bites?

    Rest assured, it's not your imagination: Several studies have shown that to mosquitoes, all people really aren't created equal. Besides factors such as heat and carbon dioxide, mosquitoes use odors to find their victims, and humans appear to exude different amounts of the volatile compounds the insects love.

    By studying mosquito behavior, entomologists are trying to tease out these favorite smells. It's a complex story, they say. Millions of years of evolution have resulted in sophisticated odor-based navigation systems that differ greatly from one mosquito species to the next, depending on where it lives and which host it prefers. Even so, chemical and behavioral studies—often using human volunteers as bait—have helped identify some of the smells that tempt several mosquito species. And recently, molecular researchers have begun identifying the receptors that pick up these odors and translate them into neural signals.

    Researchers hope to use odor cues to lure mosquitoes into the perfect trap or otherwise outwit them—say, by designing repellents that foul their sense of smell. Garden parties and golf getaways might be the first beneficiaries; indeed, one U.S. company is already marketing the $500 to $1200 Mosquito Magnet, which purportedly attracts mosquitoes by emitting a compound called 1-octen-3-ol, as well as heat, CO2, and water vapor.

    But the ultimate goal is a far cry from such pricey gadgets, says Willem Takken of Wageningen Agricultural University in the Netherlands, a pioneer in the field. He'd like a simple, $1 or $2 trap that people in developing countries could affix to their doorposts to keep out the mosquitoes that spread deadly diseases. Key targets are Anopheles gambiae, the species that transmits malaria, and Aedes aegypti, which spreads dengue and yellow fever.


    Anopheles gambiae (left) bites mainly on the feet and ankles; An. atroparvus prefers the face.


    Blood, sweat, and cheese

    For almost a century, researchers have been trying to divert mosquitoes from their pursuit of human blood. The field blossomed in the 1950s, when dozens of entomologists in several countries set out to discover what attracts females—the only mosquitoes that bite—to their hosts. Anthony Brown of the University of Western Ontario in London, Canada, for instance, built human-shaped steel tanks, which he called robots, dressed them up, and then counted the number of mosquitoes that landed on them in a forest. He found, among other things, that the robots became more attractive if their skin was 37°C (the temperature of the human body) than at lower temperatures, if they exhaled CO2, or if they wore a wet jerkin—or, better still, one soaked in human sweat.

    By the mid-1960s, most research on host attraction had stopped, in part because DDT made mosquito extermination so easy. Lately, however, emerging resistance and second thoughts about insecticide use have sparked a renewed interest in alternative control methods.

    Scouting for potentially attractive compounds, researchers are taking a closer look at the more than 300 chemicals present on human skin. Martin Geier of the University of Regensburg, Germany, for instance, takes skin rubbings and then chemically removes a certain group of compounds—say, the ketones or the fatty acids. If one group attracts mosquitoes, it can be further separated into its individual components, he says.

    To test how compelling single compounds or mixtures are, researchers use a specialized instrument called an olfactometer, whose central part is a Y-shaped wind tunnel. Two different odors are blown into the short legs of the Y; when mosquitoes are set loose at the other end, they fly upwind and, like quiz show contestants choosing between two doors, decide whether to go left or right. Researchers can also fixate mosquitoes, apply miniature electrodes to their nerves, and test whether exposing them to a whiff of some compound elicits an electrical signal.

    Recent studies have confirmed what Brown and others discovered half a century ago: that for most mosquito species, CO2, heat, and moisture are key attractants. But these lead a mosquito to any warm-blooded animal—bird, cow, or human. That might be fine for species that aren't too picky, such as Culex pipiens, a West Nile vector in the United States. But those that dine almost exclusively on humans, such as An. gambiae and Ae. aegypti, need much more specific attractants.

    Hunting for cues, Bart Knols, a researcher in Takken's group, noticed in 1995 that An. gambiae had a predilection for biting its victims on the feet and ankles—even when their entire bodies were exposed. (This clearly set it apart from related species, such as An. atroparvus, a mosquito from Holland that goes mainly for the face.) A native of the Dutch province of Limburg, Knols also realized that foot odor bears a remarkable resemblance to the pungent cheese from that region. And sure enough, An. gambiae turned out to be heavily attracted to the smell of Limburger cheese.

    The finding, after making snickering headlines around the globe, led researchers to tempt different mosquitoes. “It became sort of a madhouse,” Knols recalls. “People started taking Limburger cheese all over the world.” But the stinky dairy product turned out to be an acquired taste, he says; just those few mosquitoes that feed primarily on humans were strongly attracted.

    Knols says the common denominator between feet and cheese is obvious: a bacterium used in cheese production, called Brevibacterium linens, which is a close relative of Brevibacterium epidermis, a bug known to reside in the warm, humid clefts between human toes. Both turn glycerides into a specific set of breakdown products, such as fatty acids. Takken's group is now trying to find out exactly which products provide the draw.

    Over the years, researchers have found that individual species have their own idiosyncratic tastes for various attractants. Ae. aegypti find lactic acid—which humans produce on their skin but other mammals don't—sublime; to An. gambiae, it's only so-so. With ammonia, it's the other way around. And even in Aedes, Geier explains, lactic acid alone isn't all that attractive; rather, it boosts the appeal of several other compounds.

    Complicating matters, explains Ring Cardé of the University of California, Riverside, an effective trap depends not just on the right attractants but also on the physical properties of the odor plume. Cardé has spent most of his career studying how male moths home in on females by navigating pheromone plumes—which, from the insect's viewpoint, consist of a series of small odor filaments swirling through the air. More recent work in mosquitoes, carried out by Cardé's colleague Teunis Dekker, suggests that they, too, use the fine structure of an odor plume to navigate, and Cardé believes that the shape and structure of a plume will determine any trap's efficacy.

    Takken and others hope that molecular researchers, who joined the field just 2 years ago, will help make sense of it all. They are making some headway: In a study published on page 176, a team led by Laurence Zwiebel at Vanderbilt University in Nashville, Tennessee, has scoured the newly sequenced An. gambiae genome for so-called G protein-coupled receptors, which include odor receptors.

    The team, working with researchers at the University of Notre Dame in Indiana, the University of Illinois, Urbana-Champaign, and Celera Genomics in Rockville, Maryland, found 79 odor-receptor candidates, only five of which had been known before. Of these, 64 were expressed solely in the mosquitoes' olfactory tissues—evidence that they're probably involved in odor recognition. And at least one of the candidate receptors is produced only in mature females—an important clue that it might be involved in host seeking. So far, the group hasn't been able to link any of the odors known to attract An. gambiae to any of the receptors. Still, the study is a “nice breakthrough,” says Takken, that might speed the discovery of other, more powerful attractants.

    Death trap.

    The Mosquito Magnet's popularity is growing in the United States (bottom). Something much simpler and cheaper is needed to divert mosquitoes in developing countries.


    Building the perfect trap

    Whether chemical lures can be fashioned into an irresistible mosquito trap, much less one that would be cheap and effective in developing countries, isn't clear. But there is a precedent. In many East African countries, simple traps have helped virtually eradicate tsetse flies, the carriers of sleeping sickness and a livestock disease called nagana. (One trap consists of a simple black-and-blue cloth, baited with acetone and octenol—or, alternatively, buffalo urine—and sprayed with insecticide.)

    Mosquitoes, however, could pose a more daunting challenge. One tsetse fly produces only a handful of offspring over her lifetime, making the population vulnerable to even a slight increase in mortality. By contrast, mosquito mothers can produce hundreds of young. It might also be “very difficult,” says Geier, to produce a trap that can compete with the real thing: living, breathing humans who emit not just smell but also heat and moisture. (A trap could do that too, of course, but it would quickly get too complicated and costly.) But even if they only reduced the number of mosquitoes, “traps could have a fantastic impact,” says Takken. “We all agree that no single measure will ever solve the malaria problem completely.”

    Short of that ambitious goal, traps might also be effective in monitoring the risk of epidemics and focusing control efforts. Some countries already use a relatively unsophisticated trap developed by the U.S. Centers for Disease Control and Prevention (CDC) to keep track of pathogens. But this trap, which relies on just CO2, light, or a combination, catches a motley array of insects—often not those most relevant to human health. To catch An. gambiae, says Takken, a human needs to be nearby, and because the attractiveness of people varies, so does the nightly catch. Spiking such a trap with a specific odor blend could lead to a much better and more reproducible haul, he says.

    Other mosquito-thwarting strategies on the drawing board are clever new repellents. If, for instance, researchers could find compounds that overstimulate crucial odor receptors, they might be able to disorient the insects, dooming them to a life of aimless buzzing, Zwiebel says. It might even be possible, he says, to tinker with the receptors that help mosquitoes find nectar or places to lay their eggs.

    In the meantime, attraction studies with human volunteers suggest another, more down-to-earth approach to keeping mosquitoes at bay. Among his human subjects, chemist Ulrich Bernier of the U.S. Department of Agriculture in Gainesville, Florida, has found some people who are almost never bitten. His team has isolated compounds from their skin—he declines to discuss which ones—that he believes might be a clue to the protection. Someday, he speculates, they could serve as a natural, less toxic alternative to DEET.

    Splashing yourself or your house with somebody else's body odor might not sound all that enticing. But at the levels needed to keep bugs away, Bernier assures, humans won't smell a thing.

  18. Lab v. Field: The Case for Studying Real-Life Bugs

    1. Martin Enserink

    Molecular entomology is all well and good, some researchers say—but what about studying insects where they live and breed: in the field?

    These querulous observers don't want to sound like curmudgeons. Nor do they want to take away anyone's scientific glory. But some tropical disease researchers say they just can't get very excited about the sequence of the Anopheles gambiae genome, published in this issue of Science. To be sure, the sequence promises to reveal the inner workings of the mosquito in unprecedented detail, shedding light on everything from its metabolism to insect evolution. But skeptics aren't convinced it will actually help control malaria—or, as Chris Curtis of the London School of Hygiene and Tropical Medicine puts it, “pass the so-what test.”

    For more than a decade now, Curtis and other vector ecologists have argued that the field of insect-borne diseases—whether malaria, dengue, West Nile virus, or Lyme disease—is betting too many of its scarce research dollars on high-tech work like DNA sequencing and too few on studies of insect behavior and ecology, the type of fieldwork that gets your back sweaty and your hands dirty. To figure out how these diseases behave, they say, you have to don your boots rather than start your sequencer (see p. 87).

    The riposte from molecular researchers is that ecological studies are important, but given the lack of progress in the fight against insect-borne diseases, new strategies are needed. “If ecology had all the answers, there wouldn't be molecular biology,” says Anthony James, a molecular entomologist at the University of California, Irvine. In the past few years, the sparring has gotten especially intense over molecular biologists' boldest plan: to control malaria by releasing transgenic mosquitoes (see Morel Viewpoint on p. 79). Some ecologists have dismissed the scheme as a grandiose folly—a Star Wars of infectious disease—that is diverting money from more “down to earth” research. James chalks up part of the bickering to the “impoverished mentality” that afflicts all of tropical disease research. When funding is tight, he explains, “people start fighting over whose work is more important.”

    Sexier science

    Field studies of mosquitoes, which peaked during the vector biology heyday of the 1940s and 1950s, were dealt their first heavy blow when DDT and other insecticides promised to end insect-borne disease. By the time insecticide resistance and growing opposition to chemical use shattered that dream, the molecular biology revolution was well under way, and chasing mosquitoes in the field seemed old-fashioned and obsolete. “People just find molecular biology sexier,” concedes Duane Gubler, chief of the division of insect-borne infectious diseases at the U.S. Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado. “It's seen as the future.”

    Indeed, for the last 15 years or so, molecular scientists have dominated mosquito research grants and high-profile publications. Of more than 130 mosquito studies currently funded by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), only about one in five includes fieldwork, while DNA work booms. The World Health Organization (WHO) has also made the transgenic mosquito one of its top priorities in fighting malaria.

    The funding shift, some say, created a self-perpetuating cycle: Universities hired molecular researchers because they could pull in grants, and vector biology departments took on a decidedly molecular bent. “The molecular people are multiplying like flies,” laments Yale medical entomologist Durland Fish. Even if they would like to do field studies, he says, young scientists are forced to follow the money and end up in molecular research.

    As a result, studies that could make a dent in disease transmission are lacking, ecologists say. Dengue fever, a debilitating and sometimes fatal disease transmitted by a mosquito species called Aedes aegypti, is a case in point, says CDC entomologist Paul Reiter. Until a vaccine is available, the best way to block its continued spread is to reinvigorate mosquito-control programs, which aren't working well now, says Reiter.

    The problem, he says, is that researchers still don't know certain cornerstones of dengue vector ecology, such as the mosquitoes' longevity—a crucial factor in their ability to transmit diseases—and the relation between mosquito density and human infection risk. With better information, he adds, scant resources for vector control—insecticides, reduction of breeding sites, and biological control—could be employed more effectively.

    A similar lack of knowledge is hampering the control of West Nile virus, which landed in New York City in 1999 and has now spread across most of the continental United States, says Fish. Scientists aren't sure which mosquito species are the primary “bridge vectors” that shuttle the virus from birds to humans. It's also unclear how best to control them or the mosquitoes that infect birds, West Nile's primary hosts. But presumably, Fish says, research could identify a better alternative than sending out the spray trucks whenever citizens turn in large numbers of dead birds.

    Designer mosquitoes

    Of all the molecular projects, it's the diversion of malaria funds to the genetic engineering of mosquitoes that makes entomologists the most apoplectic. “It's pie in the sky,” says Fish. The idea is to replace natural mosquito populations with lab-engineered or transgenic cousins incapable of spreading malaria. In a major advance, a team at Case Western Reserve University in Cleveland, Ohio, showed earlier this year that it could make An. stephensi—a cousin of An. gambiae— resistant to Plasmodium infection by giving it an extra gene. If researchers can find a way to do the same in An. gambiae and also find a way to make these mosquitoes outcompete their natural counterparts, the parasite would no longer be able to propagate. “I really believe this will work one day,” says Frank Collins, a proponent of transgenics at the University of Notre Dame in Indiana.

    But ecologists say it's a long shot. Despite recent progress in engineering mosquitoes in the lab, many real-world questions remain unanswered. Will the designer mosquitoes be able to survive in the wild, for instance? Will they disperse, find mates, and have viable offspring—and if so, how long would it take for their parasite-resistance genes to spread? Would it help if resistant mosquitoes had fewer parasites in their saliva than wild ones, or would they have to be completely resistant? What portion of the population would have to become transgenic to actually make a dent in the rate of malaria transmission? And what's the risk that their new genetic baggage would transform them into vectors for other diseases? The only way to find out is to study natural mosquito populations, say the ecologists, many of whom are visibly irked that molecular biologists didn't involve them in planning the transgenic project. “There are lots of things they have never given much thought,” says Andrew Spielman, an entomologist at Harvard School of Public Health.

    “If ecologists were so eager to help, then why didn't they jump in earlier?” counter the molecular biologists.

    Ironically, some say, the controversial project might actually help bring the two sides together. Four months ago, Thomas Scott of the University of California, Davis, and Willem Takken of Wageningen Agricultural University in the Netherlands, who both study vectors in the field, assembled some two dozen of their colleagues to explore the ecological questions surrounding the transgenics plan. Only one molecular biologist was invited. Although some ecologists remained skeptical about the whole idea, most participants agreed that, because the transgenic mosquito train appears unstoppable, the best course of action is to quit griping and hop on.

    They crafted a research agenda (see Scott Viewpoint on p. 117) that includes hefty doses of mosquito population genetics and studies of mating behavior, evolution, and epidemiology. Several say they have started writing grant proposals and setting up collaborations with molecular researchers.

    The funding agencies appear receptive. WHO, for instance, might pay more attention to ecology. An August meeting of 50 scientists, charged with charting a scientific course for the tropical disease program for the next 5 years, recommended as a top priority field studies of malaria, dengue, lymphatic filariasis, and several other diseases.

    At NIAID, vector biology director Kate Aultman says she welcomes proposals for field studies. The rift between the two sides has long frustrated her, Aultman says, and fostering collaborations has been difficult. But they are essential, she notes: “Molecular biologists, bless their hearts, don't have a clue how to catch a mosquito.”

  19. An Elegant But Imperfect Tool

    1. Gretchen Vogel

    Pesticide-treated mosquito nets save lives—in the short term. But reaching people who need them most is no simple task

    BOBO-DIOULASSO, BURKINA FASO—The net is an elegantly effective trap. Drawn by the scent of a sleeping human, the female Anopheles gambiae mosquito closes in for her blood meal. But as she flies toward the human target, she runs into a web of cotton or polyester. As soon as she touches the net, a powerful insecticide numbs her legs. She might fall to the ground stunned, easy prey for lizards or ants. If she lingers, the chemical will kill her within a few seconds.

    Insecticide-treated bed nets have emerged in the last decade as one of the great hopes in the fight against the mosquitoes that carry malaria. They are technologically simple, and more than 70 studies have shown that they work. In the first year after the introduction of bed-net programs into African villages, for instance, the mortality rate for children under age 5 typically drops by 15% to 25%. Even better, several studies have shown that the neighbors of those who sleep under bed nets are also protected, presumably because the nets not only block mosquitoes but also kill them in significant numbers. Based on those promising data, the World Health Organization in 1996 made distribution of treated nets a key part of its Roll Back Malaria program. The goal: to ensure that 60% of people in malaria-endemic areas sleep under nets by 2005.

    Real life.

    Researchers from Centre Muraz in Bobo-Dioulasso conduct door-to-door surveys to find who uses mosquito nets, who doesn't—and why.


    Even so, bed nets are not the cure-all they are often touted to be, and their flaws are most evident in tropical Africa. In some parts of the continent, the malaria parasite and the mosquitoes that carry it are so thoroughly entrenched that even if bed nets killed nine out of 10 mosquitoes, residents could still receive dozens of infective bites per year—so many that the overall disease rate would remain unchanged. Logistically, getting bed nets to the poor who need them most is a huge challenge, and ensuring that the nets are retreated with pesticides every 6 months is harder still. Even if logistics were not a problem, concern is growing that mosquitoes will become resistant to bed-net chemicals, as they have to other insecticides.

    On top of these difficulties, some data suggest that, although bed nets clearly prevent malaria in the short term, they might leave children more vulnerable to the disease later in life by delaying the development of an immune response. In light of these caveats, some researchers are suggesting that money and efforts devoted to bed nets might be better spent on boosting treatment programs.

    Bed nets for sale

    The dirt roads of Bama, 45 minutes north of Bobo-Dioulasso, swarm with people on market day. Alongside neatly piled pyramids of tomatoes and mangoes, overflowing sacks of rice, and baskets of roasted black-and-yellow striped caterpillars, merchants display mosquito nets for sale. Nets are common here even though the going price—6000 West African CFA (about $8)—is enough to buy 30 kilos of rice or more than 200 good-sized mangoes. The village is on the edge of vast irrigated rice fields—a fertile spot for mosquito breeding—and villagers can receive hundreds of bites per night. Those with mosquito nets sleep much more comfortably, but some can't afford the luxury.

    Sociologist Léa Paré-Toé, entomologist Thierry Baldet, and their colleagues at the Centre Muraz in Bobo-Dioulasso are conducting door-to-door surveys and small discussion groups to find out who in Bama lacks treated nets and why. The team asks who sleeps under nets, the last time the net was treated with insecticide, and how much the residents understand about the connection between nets and malaria. In one group of 12 farmers between the ages of 20 and 49, someone suggests that eating the wrong food causes malaria. Most in the group have nets at home, but few have them treated. Only a handful have heard that bed nets can prevent malaria. Such responses are not uncommon, Paré-Toé says, and they clearly demonstrate how far public health workers have to go before Roll Back Malaria is even close to meeting its 60% target.

    The team also asks how much a person is willing to pay for a net and pesticide treatment. But in reality, says Bob Snow of the Kenyan Medical Research Institute, Nairobi, “there's an enormous gulf between willing and able to pay” for many people in malaria-affected regions. He is pessimistic about so-called social marketing strategies—advertisements promoting bed nets and their use—that rely on existing market systems to sell nets. “If you believe bed nets work, why are you asking people to pay for them?” he asks.

    Mixed blessing.

    Irrigated rice fields are important sources of income—and ideal mosquito breeding spots.


    Cost is an even more acute problem for retreatment programs. The group of insecticides that is most effective at killing mosquitoes, pyrethroids, wears off after about 6 months, or sooner if a net is washed. Nets must be dipped regularly to retain their mosquito-killing ability. Although the process is not complicated, it is one of the weakest links in bed-net programs.

    “It's hard for people to perceive an immediate benefit from treating their nets,” notes entomologist William Hawley of the U.S. Centers for Disease Control and Prevention (CDC), who studies the effects of bed nets and their use in Kenya. People are even less willing to pay for redipping than for the original nets. When researchers have offered free retreatment, participation has been relatively high. But when they charge a fairly modest sum, 50 cents, according to a study in The Gambia, participation drops to about 20% of net owners. “It's as if you held national immunization days and then said to the parents, ‘By the way, give us 50 cents to cover the cost of the shot,’” explains Richard Steketee, chief of CDC's Malaria and Epidemiology Branch, who works with Hawley in Kenya. “The immunization people would never dream of doing that.”

    A question of balance

    In light of these problems, the massive efforts under way to encourage bed-net use are in danger of being misspent, warns malariologist David Modiano of the University of Rome, who has worked with several net projects in Burkina Faso. He fears that an overemphasis on nets will divert money from programs aimed at increasing access to malaria medicines and treatment. He also warns that successful bed-net programs could have an unintended side effect: preventing children from acquiring an immunity to the parasite that could be lifesaving later on.

    Modiano points to several studies that suggest that when malaria transmission is reduced through successful bed-net programs, people's natural level of immunity—built up through exposure to the parasite—also falls. That leaves many, especially children, more vulnerable to getting sick after just a few infective bites. And because bed nets decrease but do not stop parasite transmission, after a few years of consistent bed-net use, the number of malaria cases in a village could climb again to its original level. “I am not against bed nets,” says Modiano, “but before going to a continental scale [as WHO is advocating], it should be shown that they work in the long term.” Modiano believes that the best way to reduce malaria mortality is to broaden distribution of medicines and teach health workers and parents how to recognize and treat malaria, which, after all, “is a curable disease.”

    Snow, whose own studies have shown that people who sleep under nets often have fewer anti-Plasmodium antibodies in their blood than those who don't, agrees that in certain areas, nets are of limited value by themselves. “If all things remained equal, then in some areas of very intense transmission, the effects of insecticide-treated nets may be only marginal with time,” he says. “But we would anticipate, hope, and wish that all things will not remain equal.” Technological, social, and economic gains should all make ongoing net programs more effective, Snow says. For example, two types of permanently treated nets have recently gone on the market. Such a development “would be a godsend” to net-distribution programs, he adds. And even a partially effective vaccine might boost people's immunity enough to make up for that lost by sleeping under nets.

    Some argue that bed nets are an adjunct, not a rival, to medical programs. Christian Lengeler of the Swiss Tropical Institute in Basel reasons that if health workers face fewer overall malaria cases—at least in the initial few years of a bed-net program—they can more effectively treat those that do appear. Treatment, in turn, also helps interrupt the cycle of parasite transmission. “Bed nets are a simple and elegant way of preventing part of the malaria burden, and they go hand in hand with treatment efforts,” he says.

    “The problem has been that people have seen bed nets as a panacea—the saving grace of malaria in Africa. That's not true,” says Snow. He knows only one sure-fire solution: “Malaria is an absolutely huge problem, and it all boils down to money, money, money.”

  20. Meet the Mosquitoes

    1. Martin Enserink

    Science provides a series of thumbnail profiles of interesting mosquito species, including some of the most important vectors of human disease.

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