News this Week

Science  13 Apr 2012:
Vol. 336, Issue 6078, pp. 136

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  1. Around the World

    1 - Santiago
    Patagonian Dam Moves Forward
    2 - Stockholm
    Life Science Lab Gets Fresh Funding
    3 - Geneva, Switzerland
    Beginning of End of Higgs Hunt
    4 - Pasadena, California
    Giant Magellan Telescope Tells NSF ‘No Thanks’


    Patagonian Dam Moves Forward

    A controversial $3.5 billion hydroelectric dam project in Patagonia—Project HidroAysén—won a key legal battle last week when the Chilean Supreme Court rejected seven appeals from environmentalists and local groups seeking to stop it. Opponents had asked the Supreme Court to overturn a lower court's ruling in favor of the project, which is supported by the national government.

    Protesters in Santiago oppose Project HidroAysén.


    Builders plan to erect five dams on the Baker and Pascua rivers in the pristine Aysén region, flooding about 6000 hectares. The company says the dams could produce 20% of Chile's electricity by 2020. But opponents say that the risks—including the likelihood of glacial lake outburst floods—are greater than has been acknowledged. The company has yet to win approval to build power lines for the project, which will require a 2000-kilometer-long continuous corridor from the dams to Santiago.


    Life Science Lab Gets Fresh Funding

    A groundbreaking Swedish life science research initiative will add lab space and nearly triple its ranks to 1000 investigators, thanks to newly announced infusions of funds. The private Knut and Alice Wallenberg Foundation will donate $33.4 million, and pharmaceutical company AstraZeneca will add between $5 million and $10 million annually over the next 5 years, to Sweden's Science for Life Laboratory (SciLifeLab). The Swedish government later this year will also inject more money into the 2-year-old collaboration between four of the country's universities, according to Jan Björklund, Sweden's minister for education.

    In a strategic bid to create a national life sciences powerhouse, Sweden committed $75 million in 2010 to create SciLifeLab, whose campuses in Stockholm and Uppsala focus on proteomics studies, bioimaging, and projects such as sequencing the genomes of the Norway spruce and microbes living in the Baltic Sea (Science, 14 May 2010, p. 805). “We have high ambitions,” Björklund said at a 3 April press conference in Stockholm. The new funds will enable SciLifeLab “to gather the sharpest brains and lay the foundation for new and major breakthroughs.”

    Geneva, Switzerland

    Beginning of End of Higgs Hunt

    The Large Hadron Collider


    After its annual winter shutdown, the world's highest-energy atom smasher, the Large Hadron Collider (LHC) at the European particle physics lab, CERN, resumed taking data on 5 April, running at slightly higher energy than before. So begins what should be the final chapter in the decades-long hunt for the Higgs boson, the hypothetical particle that is key to physicists' explanation of how all fundamental particles get their mass. The LHC feeds two huge particle detectors, ATLAS and CMS, that are hunting the Higgs, and last year both spotted possible signs of the particle. This year, the LHC should produce three times as much data as it did in 2011, enough to clinch the discovery—or prove that the Higgs doesn't exist. “I would imagine that some time this summer, when we have collected as much data as we got last year, we'll get a hint of which way it will go,” says Bruce Mellado, a member of the ATLAS team from the University of Wisconsin, Madison. “Either we'll confirm the excesses we saw in 2011 or we won't.”

    Pasadena, California

    Giant Magellan Telescope Tells NSF ‘No Thanks’

    A blasting site in Chile for GMT.


    The organization behind the $700 million Giant Magellan Telescope (GMT) has decided not to seek financial help from the U.S. government to build its 24.5-meter telescope. Its decision leaves the $1 billion Thirty Meter Telescope (TMT) project as the sole contender for federal support, should the government be able to afford it in the future.

    In late December, the National Science Foundation (NSF) announced that it did not anticipate having money to fund either project until sometime in the next decade. At the same time, NSF said it would offer $1.25 million over 5 years for the development of a public-private partnership plan that might lead to the building of a large telescope, if NSF were to ever have funds available.

    The GMT Organization opted out, issuing a press release on 2 April that explained it would instead seek to cultivate partnerships on its own. “The partners in the project feel that they are making such rapid progress that they have chosen to press ahead at full speed, looking to link up with the NSF at a later date when the needs of both organizations are better aligned,” the press release states.

  2. Random Sample


    A new tool is available to help doctors detect signs of Alzheimer's disease: On 6 April, the U.S. Food and Drug Administration (FDA) approved the radioactive drug Amyvid, which binds to telltale amyloid plaques in the brain. The drug has been used for years in research, including clinical trials, but FDA had held off on approving it pending more evidence that doctors would read the scans consistently.

    The Rebounding of the Lark


    The critically endangered Raso lark (Alauda razae) lives on a single desert island in the Cape Verde Archipelago. Happily, the birds have undergone a remarkable boom over the past decade, according to a paper published online this week in Animal Conservation. Since 2004, the population of the birds has skyrocketed from 65 to 1490—including a tripling in numbers last year alone—according to a team led by ornithologist Michael Brooke of the University of Cambridge in the United Kingdom. “It's unprecedented among birds,” Brooke says. The increase correlates with greater rainfall, which probably boosts the number of insects available to eat.

    Andy Symes of BirdLife International, who has reviewed the conservation status of the lark, calls the finding “fantastic news.” But he cautions that the population could easily fall if the island dries out again. Both he and Brooke recommend that a second population be established on a nearby island to help ensure that the species isn't wiped out by an unlucky event such as severe drought, disease, or new predators.

    The Research Will Go On: Spring Tides, Mirages, and Star Fields


    Ultimately, it was an iceberg that sank the Titanic on the night of 14 April 1912. But with the 100th anniversary of the sinking of the ocean liner looming, several ideas have popped up about how conditions on the north Atlantic Ocean might have helped set the stage for disaster.

    In the April 2012 issue of Sky & Telescope magazine, physicists Donald Olson and Russell Doescher, both of Texas State University in San Marcos, note that a powerful spring tide may have helped push icebergs into the ocean liner's path. On 4 January 1912, the moon—within 6 minutes of being full—was at its closest approach to Earth in 1400 years. The resulting increase in tides may have not only enhanced the calving of Greenland glaciers, but also kept the icebergs from running aground along the coasts of Labrador and Newfoundland. Instead, the researchers suggest, the icebergs drifted into the Labrador Current, reaching the shipping lanes by April.

    British historian Tim Maltin, meanwhile, argued in a National Geographic special that aired 8 April that an iceberg in the ship's path might have been all but invisible to a lookout—thanks to a “super-refraction,” a mirage resulting from the interaction of the cold Labrador Current and the warm Gulf Stream waters. The resulting atmospheric conditions, he argued, would have created a false horizon that hid the iceberg from view.

    But at least one scientific detail has been nailed down—in last weekend's rerelease of James Cameron's 1997 blockbuster Titanic (in 3D). Prompted by a “snarky” note from astrophysicist Neil deGrasse Tyson, Cameron corrected the star field over the sinking ship to reflect what a passenger adrift in 1912 at that latitude and longitude would have actually seen.

    By the Numbers

    100% Percentage of ongoing NASA missions—nine in total—that will be extended, according to its 2012 senior review.

    10 million Number of species that researchers, writing in Systematics and Biodiversity, say the ecological community should seek to inventory over the next 50 years.


    Join us Thursday, 19 April, at 3 p.m. EDT for a live chat with experts on how deep wastewater injection is triggering earthquakes around the country.

  3. Newsmakers

    Morehouse Cardiologist Tapped to Head NHLBI



    Gary Gibbons, a cardiologist and scientist at Morehouse School of Medicine in Atlanta, has been named director of the National Heart, Lung, and Blood Institute (NHLBI).

    Gibbons, 55, founded and directs a cardiovascular research institute at Morehouse that links basic science and health in minority populations. Gibbon's own lab studies how genetic variation influences vascular biology and cardiovascular disease. He will join NHLBI this summer.

    The $3.1 billion NHLBI is the third-largest of the National Institutes of Health's 27 institutes and centers. NHLBI has not had a permanent director since Elizabeth Nabel left in late 2009 to head Brigham and Women's Hospital in Boston. Gibbons was interested in the job because of his “intimate” familiarity with NHLBI—he's a longtime grantee and adviser—and his commitment to “its legacy of doing discovery science that advances public health,” he says. He plans to update the institute's strategic vision “with a renewed look that's more timely and contemporary.”

  4. Tropical Diseases

    Mystery Disease Haunts Region

    1. Gretchen Vogel

    Could the parasite behind onchocerciasis, better known as river blindness, also explain the odd “nodding” seizures in a growing number of African children?

    Desperate measures.

    Some children with nodding disease are restrained to prevent them from injuring themselves or wandering off.


    In 1959, tropical-disease expert Louise Jilek-Aall started working as a physician in Mahenge, a town in a mountainous and isolated area of southern Tanzania. She soon encountered an “astonishing” number of people suffering from epilepsy. As she investigated further, the mothers of some of the most severe cases told her their children were normal until they were around 4 or 5 years old, when they began to have seizures characterized by repeated downward movements of their heads. Jilek-Aall says the residents had a specific word for the condition, which translated literally as “nodding the head.”

    Early on, children with the nodding seizures still led a somewhat typical life. They “were running around, playing with other children. They were not discriminated against at all,” recalls Jilek-Aall, who founded an epilepsy clinic in Mahenge in 1960. By the time they reached puberty, however, they grew sicker. “They became listless. They were not eating well,” and they suffered a noticeable decline in intelligence, she says. “Then one day, the usual grand mal seizures would start,” and the children would develop a form of full-blown epilepsy.

    At that point, their prospects were grim. People with epilepsy were feared as possibly contagious, Jilek-Aall says: “They were shunned by the others. Some of them died of maltreatment.” The numbers were hard to determine, however. At the time, she says, the people in Mahenge had very traditional beliefs, and it was taboo to discuss someone who had died.

    Jilek-Aall, now a professor emeritus at the University of British Columbia, Vancouver, in Canada first described the nodding seizures in a 1964 paper. For many years, Western colleagues doubted or dismissed her reports, but no more. An apparent outbreak of a similar nodding syndrome in Uganda and southern South Sudan over the past few years has attracted many more researchers, including teams from the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), to look for possible causes. They are chasing several suspects, including a parasitic worm, but so far there's no proven culprit.

    The world media has also become fascinated, showing videos of children nodding their heads uncontrollably or staring vacantly as if in a trance, a state that often follows the head-nodding attacks. Because food seems to trigger the attacks, many can't eat properly and quickly lose weight. Gradually, they become more and more disabled. News accounts have described how families tie their children to trees so that they don't wander off or fall into fires or rivers. Yet many do have deadly accidents; others die of malnutrition or secondary infections.

    How many children are affected in Uganda and South Sudan, as well as the exact geographic scope of the problem, are unclear. The Ugandan ministry of health has said that at least 3000 children there have nodding disease. In South Sudan, cases have been reported in six counties. The pattern of reports suggests the syndrome may be spreading, but no one has systematically surveyed the entire area, and accurate counts are difficult to achieve.

    The condition has become a prominent issue in Uganda's volatile politics, exacerbated by long-standing tensions between the northern regions and the central government in Kampala. Legislators have had heated debates over special funds to help nodding syndrome patients. And President Yoweri Museveni made two visits in March to health centers in the north that treat nodding syndrome patients. He pledged that he would defeat the disease just as he had defeated rebel warlord Joseph Kony and his Lord's Resistance Army, which terrorized northern Uganda for more than a decade.

    But without a clear explanation of the condition's cause or effective treatments, that will be no easy task.

    A new phenomenon

    Northern Uganda and the southern tip of South Sudan are notoriously difficult places to live. Both regions have been torn by decades of civil war. In northern Uganda, tens of thousands of children were kidnapped and pressed into service in Kony's army. A series of Sudanese civil wars, which culminated in South Sudan's independence last July, displaced an estimated 5 million people and killed 2.5 million. Malnutrition and a host of endemic diseases are widespread. Health services are scarce.

    A head-nodding syndrome similar to the one Jilek-Aall had described in Tanzania in the 1960s began showing up in South Sudan in the early 1990s. Then, in 2009, increasing numbers of children with head-nodding seizures began to draw the attention of health officials in northern Uganda. Residents in the area said they had never before seen such behavior. Ugandan officials asked CDC for help.

    CDC researchers were puzzled, says Scott Dowell, a pediatric infectious disease specialist who directs CDC's Division of Global Disease Detection and Emergency Response. When the call went out for qualified groups to help, “everyone said, ‘This is really fascinating, but it's definitely not one of ours,’” he recalls. Dowell's usual job is to coordinate the logistics for the experts responding to various outbreaks, but since there weren't yet any experts on nodding disease, he says, “I had the chance to go myself.”

    Dowell helped assemble a team that included epidemiologists, toxicologists, nutrition experts, and neurologists from CDC, WHO, and the Ugandan ministry of health. The researchers conducted a variety of studies, including electroencephalography (EEG) and magnetic resonance imaging (MRI) of patients' brains, sometimes during seizures. The team went in “with an open mind” about whether the nodding might be a muscular disorder or even a behavioral syndrome, Dowell says. But patients' brain-wave activity on the EEGs “made it quite clear that [head nodding] was a seizure,” and that most patients had ongoing seizure activity typical of epilepsy. The MRI scans added more evidence. “Something is badly wrong with the brains of these kids, and it's physiological,” he says.

    The researchers came together two more times in Uganda, and in May last year they visited South Sudan to investigate recent cases there. But they haven't yet figured out what is causing the condition. When WHO experts investigated a cluster of nodding disease cases in southern Sudan between 2001 and 2003, their early guesses for a cause included leftover munitions, measles, donated seeds treated with pesticides that were eaten instead of planted, donated food that might have been contaminated with toxic fungus, and even consumption of monkey meat. None of those turned out to be a clear culprit, says Abdinasir Abubakar, head of communicable disease surveillance and response for WHO in South Sudan. The region affected by nodding syndrome has actually received less food aid than other areas. “This is the bread basket of the country,” he says. And comparisons of children with nodding syndrome and their healthy peers found no association with eating donated food, Dowell says.

    Exposure to munitions doesn't seem to be the cause, either. There were other regions where fighting and bombardments were much heavier, Abubakar says, and “they have no sign of nodding disease.” The South Sudan and Ugandan cases of the syndrome do seem to have a geographic component, however. They are concentrated in a few relatively small areas. And previously healthy children who are forced to move to those areas by fighting suddenly become vulnerable to the syndrome. An influx of displaced families into affected locales is one likely reason the number of cases has gone up recently, Abubakar says.

    Geographic puzzle.

    Areas affected by nodding disease.

    The researchers have tested for a host of viruses, says CDC neuroepidemiologist James Sejvar, another team member. All tests have turned up negative. And although prion-triggered brain damage, perhaps due to eating monkey meat, has been floated as a possibility, the condition doesn't look like a typical prion disease, Sejvar says.

    One environmental factor still on the table is vitamin B-6 deficiency. A recently discovered genetic condition that prevents the body from processing B-6 causes a particularly severe form of epilepsy that doesn't respond to the usual antiepileptic drugs, Dowell says. The association with nodding syndrome isn't perfect: It isn't always children with the lowest levels of B-6 who have the symptoms, he says. But the clue is strong enough that the CDC team plans to distribute high-dose vitamin B-6 supplements as part of a proposed clinical trial to find a treatment. That trial still needs approval from ethical oversight committees in the United States and Uganda, Sejvar says, but the researchers aim to start recruiting participants this summer, ultimately enrolling 80 children. One group would receive the high-dose B-6 supplement; other participants would receive one of two antiseizure medications or a placebo.

    Ray of hope.

    Louise Jilek-Aall and her colleagues have treated thousands of epilepsy patients at the clinic she founded in Mahenge, Tanzania. Her autobiography, Call Mama Doctor, describes her half-century of work in the region.


    Fear the worm

    What that clinical trial won't address is the other leading hypothesis for the cause of nodding disease: an infection with the parasitic worm Onchocerca volvulus. The parasite is endemic in the regions that report nodding disease, and studies in Uganda and South Sudan have found that infection with the parasite is significantly more common in people with nodding syndrome than in their unaffected peers. Still, the O. volvulus connection isn't clear-cut. “The puzzling thing is that [the parasite] is widespread, but nodding is not,” Dowell says. However, he says, the association “won't go away, even though people keep saying it doesn't make sense.”

    O. volvulus is no stranger to tropical-disease experts. It causes onchocerciasis, more commonly known as river blindness. Black flies, which breed in fast-flowing rivers, transmit O. volvulus's larval worms, which take up residence under the skin of black fly bite victims and grow to adulthood. The adult worms produce microfilariae, which reside mostly in the skin and connective tissue but are also sometimes found in blood, urine, and the eye. Microfilariae can damage eye tissue so severely that untreated infections can cause blindness. An international eradication campaign launched in 1974 has eliminated the parasite from large swaths of west Africa, but it persists in 27 countries in sub-Saharan Africa and six in Latin America.

    Those who study river blindness have had a long-running debate over whether infection with the parasite might also cause epilepsy. Jilek-Aall says she suspected for years that the region's unusually high rate of epilepsy and onchocerciasis were connected, but it took 10 years before she and Erich Schmutzhard, a neurologist and tropical-medicine specialist at the University of Innsbruck, were able to address the question directly. Given the international efforts to eradicate river blindness, Schmutzhard says, many grant reviewers asked, “Why should we fund studies of a dying disease?”


    James Sejvar (left) of CDC and Abdinasir Abubakar of WHO examine a child with nodding syndrome in South Sudan.


    Finally, in 2005, armed with funds from the Savoy Epilepsy Foundation in Canada and private donations, the researchers carefully categorized 62 Tanzanians with head-nodding seizures—the most thorough study to date of the disorder. Some had only head nodding; others had more severe epilepsy with other types of seizures. They analyzed blood and cerebrospinal fluid (CSF) from most of the patients. A subset traveled the 16-hour journey to Dar es Salaam, where they underwent MRI and EEG analysis.

    The researchers reported in 2008 in Epilepsia that 43 of 51 patients tested either had microfilariae in their skin or tested positive for O. volvulus DNA using PCR. A positive PCR test was also weakly associated with brain lesions that showed up on the MRI scans. However, PCR tests on the CSF showed no traces of the parasite's DNA. The researchers concluded that the parasite could be involved in the head nodding but probably wasn't invading the central nervous system directly.

    The hypothesis took a blow, however, when a follow-up study involving 300 individuals in Tanzania, published in 2010 in Parasitology, found no correlation between the intensity of O. volvulus infection and epilepsy. (About a third of the epilepsy patients in the study had head-nodding seizures.) That was enough to persuade Schmutzhard that nodding disease remains unexplained. Based on current evidence, he says, “onchocerciasis does not cause epilepsy.”

    But Jilek-Aall is not so sure. The studies failed to find a definitive link between onchocerciasis and nodding, but they don't rule it out either, she says: “I am convinced that somehow it is connected.” Andrea Winkler, a neurologist at the Technical University of Munich in Germany who was corresponding author on both studies, agrees that the issue isn't settled. “We have not eliminated the possibility” that O. volvulus plays an indirect role, she says.

    Other researchers who have seen similar cases of head nodding also suspect the worm. In 1998, pediatric neurologist Christoph Kaiser, now based in Baden-Baden, Germany, and his colleagues reported that at least 15 of the 91 epilepsy patients they studied in the Kabarole district in Western Uganda had head-nodding seizures. The evidence that onchocerciasis can trigger epilepsy is persuasive, Kaiser says, but proving the connection has been difficult, in part because many studies simply check for microfilariae in the skin. Ivermectin, the drug distributed as part of the ongoing treatment campaigns, eliminates microfilariae, he says, but “the damage to the brain persists.”

    There are several ways that O. volvulus infections could damage the brain. In especially intense infections, the microfilariae reach the bloodstream, says parasitologist Michel Boussinesq, who studies onchocerciasis at the University of Montpellier in France, and in Cameroon. From the bloodstream, he says, they could enter the brain and cause damage directly. The lack of evidence for the parasite in the Tanzanian patients' spinal fluid argues against that, Boussinesq admits, but he says a definitive answer would come from autopsies of those who die with nodding disease. Although autopsies are difficult in hot climates and many places in Africa have local taboos against disturbing the dead, such patient autopsies “are being attempted” in northern Uganda, Sejvar says.

    Another possibility is that infection with O. volvulus triggers an autoimmune reaction. Antibodies produced to fight the parasite could also attack brain cells. There is evidence, Winkler notes, that antibodies for O. volvulus can cross-react with retinal cells. It is also possible that subtypes of the parasite could explain why head-nodding seizures seem to affect only certain regions. Winkler notes that it is widely accepted that the “savanna type” O. volvulus causes blindness more often than the “forest type,” which primarily causes skin symptoms.

    The most likely explanation for the disease, say several of the scientists chasing the disorder, is a combination of factors. Malnourished children deficient in vitamin B-6 might be particularly susceptible to neurological symptoms when they are infected with O. volvulus, for example. “Epilepsy is very often multifactorial,” Boussinesq says. “Onchocerciasis could be a needed factor but not sufficient to provoke the condition.”

    New clues could come from blood and urine samples that the CDC team collected from patients in South Sudan and Uganda. They are almost done assessing vitamin levels, possible heavy-metal exposure, traces of thiocyanates (a sign of low-level cyanide poisoning due to eating improperly prepared cassava), and genetic markers among patients and healthy controls. More comprehensive surveys of where and how many children have nodding syndrome are also planned in both Uganda and South Sudan. That should give a better picture of whether and how the syndrome is spreading.

    One crucial problem, Abubakar says, is that nodding syndrome, as terrible as it is for the people and communities that are affected, is only one of many competing health emergencies in the region. In South Sudan, already overstretched health workers are also dealing with ongoing armed clashes and an acute outbreak of kala azar, or leishmaniasis, which has infected at least 22,000 people and killed nearly 1000 since late 2009. He says he hopes the recent publicity surrounding nodding syndrome will attract more researchers to the region. “I hope the advocacy and media might inspire some more institutions who might want to come and help figure out what is going on.”

  5. Physics

    Sparks Fly Over Shoestring Test Of ‘Holographic Principle’

    1. Adrian Cho

    A team of physicists says it can use lasers to see whether the universe stores information like a hologram. But some key theorists think the test won't fly.


    Student Benjamin Brubaker tinkers with the Fermilab holometer.


    BATAVIA, ILLINOIS—The experiment looks like a do-it-yourself project, the scientific equivalent of rebuilding a 1983 Corvette in your garage. In a dimly lit, disused tunnel here at Fermi National Accelerator Laboratory (Fermilab), a small team of physicists is constructing an optical instrument that looks like water pipes bolted to the floor. Three scientists huddle within a makeshift tent—really a plastic sheet the size of a tablecloth—to install a high-precision mirror. Nitrogen from a tank flows under the plastic to keep the mirror clean. “It doesn't look very impressive, but it's the equivalent of a class 100 clean room—the best you can buy,” says Craig Hogan, a theorist at Fermilab and the University of Chicago in Illinois.

    A ratchet clicks as a physicist inside the tent tightens a bolt. Another shouts, “The front one, not the back one! The front one, not the back one!” As implausible as it seems, the homey experiment could revolutionize scientists' conception of the fabric of the universe—if Hogan is right.

    Known as the Fermilab holometer, the experiment aims to test one interpretation of the so-called holographic principle. The principle states that the amount of information that can be crammed into a region of space and time, or spacetime, is proportional to the region's surface area. That's odd, as after all, the number of computer hard drives that fit in a room increases with the room's volume, not the area of its walls. If the holographic principle holds, then the universe is a bit like a hologram, a two-dimensional structure that only appears to be three-dimensional. Proving that would be a big step toward formulating a quantum theory of spacetime and gravity—perhaps the single biggest challenge in fundamental physics.

    The principle implies a kind of information shortage that, in Hogan's interpretation, makes it impossible to say precisely where an object is. “Think back to kindergarten; you know that something is either here or it's there,” Hogan says. “It's so obvious that it's not clear that [position] is a mystery.” In fact, Hogan says, position is inherently uncertain, and the holometer aims to prove that point.

    All the experiment takes is a couple of million bucks, two lasers, and a few months of work. That makes the holometer an unusual project for Fermilab, a particle physics lab where scientists typically work on huge accelerators and hundred-million-dollar experiments that run for years. “The beauty of it is that we have the people who can come up with this low-risk, high-reward experiment,” says Fermilab's Raymond Tomlin. “It's one shot, and if you discover something you go to Stockholm [to collect a Nobel Prize]. And if you don't see anything, you set a limit.”

    Not everyone cheers the effort, however. In fact, Leonard Susskind, a theorist at Stanford University in Palo Alto, California, and co-inventor of the holographic principle, says the experiment has nothing to do with his brainchild. “The idea that this tests anything of interest is silly,” he says, before refusing to elaborate and abruptly hanging up the phone. Others say they worry that the experiment will give quantum-gravity research a bad name.

    Black holes and causal diamonds

    To understand the holographic principle, it helps to view spacetime the way it's portrayed in Einstein's special theory of relativity. Imagine a particle coasting through space, and draw its “world line” on a graph with time on the vertical axis and position plotted horizontally (see top figure, p. 148). From the particle's viewpoint, it is always right “here,” so the line is vertical. Now mark two points or events on the line. From the earlier one, imagine that light rays go out in all directions to form a cone on the graph. Nothing travels faster than light, so the interior of the “light cone” contains all of spacetime that the first event can affect.

    Similarly, imagine all the light rays that can converge on the later event. They define another cone that contains all the spacetime that can influence the second event. The cones fence in a three-dimensional, diamond-like region. According to special relativity, all observers will agree about which points are inside or outside the diamond, no matter how they are moving. The holographic principle states that the amount of information that such a “causal diamond” can hold varies with its surface area.

    That might seem like a perverse idea, but it follows from physicists' analysis of black holes. A black hole is a region of extremely strong gravity produced when, for example, a star collapses to a point, cramming an enormous mass into an infinitesimally small volume. Within a certain distance of the point, gravity grows so strong that even light cannot escape.

    That distance defines a sphere in space called the “event horizon.” In the 1970s, theorists deduced that the amount of information contained in a black hole depends on the surface area of its horizon. One bit of information—which can be 0 or 1—can be encoded in each “Planck area,” an area smaller than 10−69 square meters. Jacob Bekenstein of the Hebrew University in Jerusalem and, independently, Stephen Hawking reached that conclusion when they realized that a black hole must have an entropy—a measure of how disordered it is inside—that grows with the surface area of its event horizon. The more disordered something is, the more information it takes to fully describe it, so the information-area link follows in step.

    Known as the Bekenstein bound, that entropy limit would serve as a cornerstone for any theory of quantum gravity, which theorists expect to kick in at length scales shorter than the so-called Planck length—roughly 10−35 meters—and time scales shorter than the Planck time, about 10−43 seconds. It might have implications far beyond the event horizons of black holes, too. In the 1990s, Susskind and Gerard t'Hooft, a theorist at Utrecht University in the Netherlands, argued that any properly defined region of spacetime will obey the same information-area link, a conjecture that Susskind dubbed the holographic principle.

    No one has proved that the principle holds. However, no one has come up with a scenario in which it doesn't, says Raphael Bousso of the University of California, Berkeley, who showed how to make the principle jibe with special relativity. For example, suppose you try to exceed the bound by encoding information in individual photons and cramming ever more of them into a region. You'll end up creating a black hole well before you break the limit, Bousso says.

    Hogan's interpretation takes matters a long step further. If the area-information link holds, then a region of spacetime can hold less information than it could if the amount of information grew with its volume. The shortage implies that positions in perpendicular directions are no longer independent variables, Hogan argues. The more precisely experimenters measure an object's position in one direction, the less precisely they can know its position in a perpendicular direction. That tradeoff resembles the one imposed by the famous Heisenberg uncertainty principle, which limits an observer's ability to measure both the position and the momentum of a quantum particle.

    Specifically, Hogan argues, if researchers know precisely how far away a thing is, then they can't know exactly where it is side to side. That uncertainty should produce a sideways jiggling that grows with the distance to the object, he predicts. That jitter is precisely what physicists hope to observe with the holometer.

    The idea.

    Together, light rays emanating from an earlier event and those converging on a later one form a “causal diamond.” The holographic principle says that such a region can hold an amount of information proportional to its surface area.

    The experiment.

    If there's quantum uncertainty in spacetime, nested interferometers should jitter in unison; back-to-back ones, independently.


    Playing with the LEGO LIGO

    Physicists at Fermilab plan to measure the jitter using store-bought technology, spare lab space, and a $2.5 million grant from the Department of Energy won for the project by Fermilab's Aaron Chou. That's a mere pittance at a lab that's planning billion-dollar projects. “These huge projects take a long time to design and a longer time to fund, and I worry that by the time one gets built it might not be the most interesting thing in the field,” Chou says. “I try to keep an eye out for things that might be done more easily.”

    To spot the predicted jiggling, physicists are building a pair of L-shaped instruments called interferometers. An interferometer splits an incoming beam of laser light in two using a cube of glass called a “beam splitter.” The two beams race down the interferometer's perpendicular arms and reflect off mirrors at the ends. If the lengths of the arms are set just right, then the returning light waves will overlap and interfere so that all the light exits through the same face of the beam splitter that it entered. But if the relative lengths of the arms change, then some light will leak out of the perpendicular face, or “dark port,” allowing physicists to compare the arms' lengths to a fraction of an atom's width.

    An interferometer can also measure the sideways motion of the beam splitter. If the beam splitter moves sideways relative to one of the mirrors, it must necessarily move either toward or away from the mirror in the perpendicular arm, changing that arm's length and letting light leak out of the dark port. So in principle, experimenters can test Hogan's prediction by monitoring the output of a single interferometer for “holographic noise,” an unquenchable jitter in the beam splitter's position at frequencies of millions of cycles per second.

    Actually, the team will monitor two interferometers, Chou says. Nested side by side like spoons, the devices will sample the same region of spacetime (see bottom figure, p. 148). That's because in the time that it takes light to bounce through the devices, the causal diamonds of the two beam splitters will overlap. As it is spacetime itself that is fluctuating, the jiggling of the two beam splitters should then be correlated, making it easier to detect a tiny signal—a standard trick from the processing of radio signals. If researchers do see correlated jitter, they can also reconfigure the two devices to sit back to back and sample different regions of spacetime. Any signal from holographic noise should then go away. In the search for a signal, “we'll get a yes or a no,” says Stephan Meyer, an experimental cosmologist at the University of Chicago. “There won't be a maybe.”

    The setup should be incredibly sensitive, Hogan says. If, for any reason, the two beam splitters move in concert by roughly a Planck length per Planck time, then experimenters should be able to detect the motion that accumulates in the fraction of a microsecond it takes light to pass through the apparatus. So the experiment will be able to search for effects on the so-called Planck scale, regardless of their origins. “That's why experimentalists love it,” Hogan says.

    For a particle physics lab, the holometer experiment is a string-and-sealing-wax affair. Only one of each interferometer's two 40-meter arms will fit in the tunnel. To house the other two arms, researchers have run plastic pipes through the side of the tunnel and the earthen berm that covers it to a wooden shed that resembles an outhouse. The experiment runs out of trailers that may have been new when Ronald Reagan was president.

    The holometer team is also borrowing technology. Team members Rainer Weiss and Samuel Waldman of the Massachusetts Institute of Technology in Cambridge also work on the Laser Interferometer Gravitational-Wave Observatory (LIGO), which comprises interferometers in Hanford, Washington, and Livingston, Louisiana, each with 4-kilometer-long arms. They've advised their Fermilab colleagues how to build their instruments with store-bought parts, says Fermilab's Chris Stoughton. “The LEGO LIGO was our catch phrase,” he says. “You didn't need to build a big experiment; you just needed to buy the parts and reconfigure them differently.”

    The holometer project also gives the particle physicists a rare treat: a chance to work in a small team. “This is one of the few experiments where you can get your hands on—and your head around—every part of the experiment,” says Robert Lanza, a graduate student at the University of Chicago.


    At the least, the experiment will probe the Planck scale, originator Craig Hogan says.


    Wanna bet?

    But will the holometer really test the holographic principle? Aptly enough, uncertainty is high.

    Even Hogan acknowledges that his prediction of an observable jittering isn't airtight. He assumes that the uncertainty relationship applies to the position of a macroscopic object. But it could apply just to the subatomic particles within the object, which would produce a much smaller effect. In that case, failure to spot the quivering wouldn't torpedo the basic holographic principle, Hogan says. “If we don't see a signal, nobody is going to abandon these ideas of holography,” he says. “On the other hand, if we do see a signal, it will make the whole idea of holography more concrete.”

    But some experts on the holographic principle think the experiment is completely off-target. “There is no relationship between the argument [Hogan] is making and the holographic principle,” Bousso says. “None whatsoever. Zero.” The problem lies not in Hogan's interpretation of the uncertainty relationship, but rather in “the first step of his analysis,” Bousso contends.

    Bousso notes that a premise of special relativity called Lorentz invariance says the rules of physics should be the same for all observers, regardless of how they are moving relative to one another. The holographic principle maintains Lorentz invariance, Bousso says. But Hogan's uncertainty formula does not, he argues: An observer standing in the lab and another zipping past would not agree on how much an interferometer's beam splitter jitters. So Hogan's uncertainty relationship cannot follow from the holographic principle, Bousso argues.

    The experiment can do no good in testing the holographic principle, Bousso says, but running it could do plenty of harm. The holometer has garnered an inordinate amount of attention in the blogosphere and in press accounts, he says, raising unrealistic expectations. “They're not going to have a signal and then there is going to be a backlash saying that the holographic principle isn't valid, and we'll look like we're on the defensive,” Bousso says. “That's why I'm trying to get the word out [that the experiment won't test the principle] without appearing to make excuses.”

    Hogan is unruffled. He sticks by his claim that the holographic principle implies an uncertainty in position that may be observable. This uncertainty relationship violates Lorentz invariance, he acknowledges, but the bigger issue is how Lorentz-invariant spacetime itself emerges from deeper physics at the Planck scale. In any case, Hogan says, debating this experiment can only benefit the field of quantum-gravity research, which has remained essentially theoretical. “If we can actually have an argument about an experiment and whether or not we're doing a test of something, I think that's helpful,” he says.

    At the least, the experiment will probe the Planck scale in some way, Hogan says. “What I would love is for theorists to predict that we won't see anything,” he says. “They haven't done that.” Then again, they don't have to. Within a year, Hogan and his team will have their data. It would make a thrilling, feel-good story if they scored a huge discovery that served as the basis for a real theory of quantum gravity. In science, however, long shots pay out even less often than they do at the racetrack.

  6. Lunar and Planetary Science Conference

    Icy-Hot Mercury's Water Pinned Down in the Dark

    1. Richard A. Kerr

    At the meeting, researchers heard that signs from the MESSENGER spacecraft orbiting Mercury strongly support the claim that the planet's polar regions harbor eons-old stores of water ice.

    Good fit.

    Radar reflections (white) from water ice coincide with cold, shadowed regions (black)


    Lead may melt in Mercury's noontime sun, but for 2 decades, planetary scientists have suspected that the polar nooks and crannies of the innermost planet harbor eons-old stores of water ice. At the meeting, researchers heard that signs from the MESSENGER spacecraft orbiting Mercury strongly support that claim.

    Water ice had been the leading explanation for the spotty but bright radar reflections from the polar regions of Mercury since Earth-based radar first detected the reflections in 1991. Radar beams reflected from the spots the way they do from the water-ice cap of Mars. And the bright reflections came from inside large, high-latitude craters—places where perpetual shadows might chill the ground enough to preserve water ice for eons.

    To detect any possible water ice, MESSENGER carried the first neutron spectrometer to probe Mercury. Cosmic rays striking the planet's surface send neutrons flying into space. But the hydrogen of water ice could keep some neutrons from reaching MESSENGER. Planetary scientist David Lawrence of The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, and his colleagues reported that MESSENGER's neutron spectrometer had detected 1% fewer fast neutrons streaming from the north polar region than from the equator. Nearly pure water ice buried under a few tens of centimeters of insulating rocky soil could be responsible for the neutron decrease, Lawrence said.

    As the first Mercury orbiter, MESSENGER is also getting the closest look ever at the shadows cast near the north pole. As planetary scientist Nancy Chabot of APL and her colleagues reported, MESSENGER imaging has revealed that near the north pole, nearly every crater wider than 10 kilometers strongly reflects radar, as water ice does, and the radar brightness essentially coincides with permanent shadow. “That's really striking,” she said.

    Perhaps the most striking support for the water-ice theory was the combination of the newly determined shape of Mercury's surface and a model that keeps track of incoming solar energy. MESSENGER's laser altimeter revealed the north polar region's crater-strewn topography in fine detail. Planetary scientist David Paige of the University of California, Los Angeles, and his colleagues folded that topographic map into their model, which calculates the amount of heating by sunlight. It computes surface and subsurface temperatures by gauging where permanent shadows are cast and how much sunlight is reflected into those shadows, among other processes.

    The model's calculated temperatures alone are “fairly conclusive” evidence that water ice dominates Mercury's radar-bright deposits, Paige said. Model temperatures beneath 10 centimeters of insulating soil in permanent shadow typically run about 100 K. That is just the temperature needed to preserve water ice for billions of years against sublimation to space, Paige noted. Other candidates for radar-bright deposits, such as sulfur, would survive at higher temperatures, but the modeling indicates that those temperatures are rare in the deposits.

    Considering all lines of evidence, “I think the case is strong now” for water ice on Mercury, says planetary scientist Dana Hurley of APL, who was not involved in any of the analyses. In fact, “it could be that Mercury is in the sweet spot” for retaining the water of impacting comets.

    Inside Mercury's permanent shadows, it is cold enough that water vapor from impacting comets will freeze to the surface but warm enough that some of the surface ice will diffuse downward before it is lost. Under some insulating soil, it is colder still, just cold enough to preserve the ice for eons. The moon's cold shadows are actually too cold for much deep storage, making Mercury the more productive icemaker.

  7. Lunar and Planetary Science Conference

    Tougher Times for Any Life on an Early Mars?

    1. Richard A. Kerr

    In the meeting's sole plenary lecture, a planetary geologist marched back in martian time to argue that Mars has always been cold and dry.

    James Head is looking to dry out and freeze up the planet Mars. While his fellow planetary scientists have been haltingly moving away from visions of a “warm and wet” early Mars conducive to the origin of life, Head has been building a case that Mars has been bitterly cold and hyper-arid for almost all of its 4 billion years. A few splashes of cold running water lightly carved the surface several billion years ago, he allows, but otherwise the surface, at least, of the Red Planet has most likely never been a place for life.

    In the meeting's sole plenary lecture, Head, a planetary geologist at Brown University, marched back in martian time. He drew from the geologic climate record revealed by orbiting cameras and roving instruments, supplemented by global models of martian climate. The past 3.5 billion years of Mars climate was straightforward enough. On the surface, most researchers agree, ice moved back and forth between the poles and lower latitudes as the planet's wobbly rotation axis let the sun alternately warm the poles and the equator. But there was no rain and only rare trickles of glacial meltwater.

    Next, Head argued that the martian climate of the eon before 3.5 billion years ago was probably much the same: almost always cold and dry. No one has found a satisfactory way that early Mars could have warmed above the freezing point for hundreds of millions of years at a time, he noted. And he pointed to emerging signs that Mars was, in fact, quite cold. For example, from glacial landforms, Head and colleagues have deduced a mean annual temperature at midlatitudes of less than 0°C about 4 billion years ago. That's well back into what has been considered warm and wet, or at least continuously damp.

    Of course, many of the ancient terrains of Mars look as though they were once awash, but those watery markers could have been created without persistent surface warmth and wetness, Head said. True, clays now commonplace on the surface require prolonged contact of liquid water with rock. But researchers have lately found that at least some clays likely formed well below the surface, he said. Surface features like lakebeds and networks of branching river valleys now appear to have formed geologically quickly during brief episodes warm enough to melt snow and ice. And Mars might have warmed briefly about the same time, when humongous but episodic volcanic eruptions spewed greenhouse gases.

    Head and the rest of the planetary science community could soon have a chance to test his perpetually-cold-and-dry scenario. The Curiosity rover will plunge into the martian atmosphere 5 August to land by a neatly exposed geologic record of the traditionally interpreted shift from a warm and wet to a cold and dry Mars.

  8. Lunar and Planetary Science Conference

    Snapshots From the Meeting

    1. Richard A. Kerr

    Snapshots from the meeting include martian features that behave just like areas of Antarctica that are known to be wet and evidence that the LCROSS lunar impacter most likely struck a particularly wet spot by chance.

    Earthly dampness.

    Water flowing in the soil of Antarctica leaves Mars-like surface markings.


    A wet Antarctic link to Mars. At last year's conference, Mars Reconnaissance Orbiter team members presented some intriguing images. They appeared to show where water had just dribbled down martian slopes, dampening and darkening as it went (Science, 15 April 2011, p. 303). This year, planetary scientist Joseph Levy of Oregon State University in Corvallis compared how fast those martian dark streaks progressed downhill with how fast water from melting ice and snow in Antarctica's Taylor Valley oozed through the ground and wicked to the surface to create a lengthening dark streak. The martian features behaved just like those terrestrial features known to be watery. Even the calculated martian soil permeability was much the same, like that of very fine sand. Any implications for life on Mars? An Antarctic wet streak “is a tough place to make a living,” Levy says, “but something does”: bacteria and hardy algae.

    A lucky shot at the moon? After a precisely targeted impacter plowed into the moon in October 2009, the first Science headline was “The Moon Is Wet!” True enough: The LCROSS spacecraft did detect abundant water in the impact's debris (Science, 19 March 2010, p. 1448). But “I think LCROSS got lucky,” LCROSS team member Richard Elphic of NASA's Ames Research Center in Mountain View, California, said at the meeting. In the 1990s, the Lunar Prospector orbiter measured lunar hydrogen in water by detecting neutrons flying off the moon. If all of the moon's permanently shadowed, deeply chilled areas harbor as much ice as LCROSS found, Elphic and his colleagues calculated, Lunar Prospector would have detected 10 times as much water hydrogen as it actually did. Although the LCROSS impacter was indeed guided to a broad area enriched in water, Elphic says, it most likely struck a particularly wet spot by chance.

  9. Lunar and Planetary Science Conference

    The Young Solar System Took a One-Two Punch?

    1. Richard A. Kerr

    A planetary dynamicist suggested that those who believe the early geologic record reflects the solar system's violent birth pangs and those who see evidence of a "late heavy bombardment" might both be partly right.

    How violent were the early days of the solar system? For 40 years, scientists have debated when and how badly the rocky inner planets were battered in their youth. Some think any pounding recorded in the early geologic record was just the dwindling away of the solar system's violent birth pangs. But others, sometimes called catastrophists, see evidence that a brief “late heavy bombardment” by mountain-size bodies shook things up again about 4 billion years ago. At a preconference workshop, planetary dynamicist William Bottke suggested that each group might be partly right.

    Bottke models orbital dynamics at the Southwest Research Institute (SwRI) in Boulder, Colorado. Drawing on numerous presentations at the earlier 75-attendee bombardment workshop, which he co-organized, he tried to understand why dating impacts on the moon, Earth, and asteroids has been so confusing. Some dating techniques seem to show a 4-billion-year-old spike; others don't.

    The beginning.

    Debris left from planetary formation later pummeled the solar system, possibly twice.


    At the conference, Bottke, with SwRI colleague Simone Marchi and others, reported that part of the problem may be that there are two kinds of impacts. “Slow” impacters hit at about 18,000 kilometers per hour, a speed typical of collisions in today's asteroid belt. Fast impacters move at 65,000 kilometers per hour, delivering 1000 times the impact energy of slow impacters. Because only high-speed impacts have the energy to reset the argon-argon isotopic “clock” often used to date impacts, the group noted, the argon-argon method lets most slow impacts go unrecorded.

    At the conference, Bottke presented a blend of the competing bombardment histories that takes account of the spotty impact record produced by a mix of fast and slow impacters. As all agree, a few hundred million years after solar system formation, the lower-energy tail end of debris left over from planet formation thudded slowly through the solar system. But then, starting roughly 4.2 billion years ago, Jupiter and Saturn plowed inward through the young solar system, gravitationally stirring up high-energy impacters, Bottke said. That planetary migration is the leading candidate for triggering any late bombardment.

    Bottke thinks the resulting late bombardment was longer and less intense than many catastrophists have proposed. That's because the planetary migration created a bunch of high-energy impacters that were slow to escape the asteroid belt and hit the inner planets (Science, 15 April 2011, p. 302). Although harder to detect today, Bottke said, the stretched-out “spike” would have been “pretty heavy” and catastrophic.

  10. Computational Biology

    Virtual Hot Spots

    1. Elizabeth Pennisi

    Physiological ecologists who design computer models to predict how animals handle heat are forecasting the effects of climate change.

    Computational Biology in-article table of contents

    When he was a graduate student in ecology, Warren Porter spent a year in the field watching desert iguanas. Yet a simple question continued to puzzle him: Why did the color of this lizard's skin get lighter during the day? After Porter landed a position in the zoology department of University of Wisconsin, Madison, as an assistant professor, he looked outside his field for answers. He started taking engineering courses to learn about heat transfer and other physical principles that affect animals, and eventually teamed up with two mechanical engineers to build a computer model to test how differently colored lizards would fare as the sun made its way across the sky.

    “We found that brightening would extend their activity by 2 to 3 hours a day or more,” Porter recalls. The lighter skin absorbed less heat, reducing the likelihood of overheating, and that translated into extra time for foraging. The result sold Porter on the value of computer modeling.

    Thirty years later, this biophysical ecologist still sits down at the keyboard to predict how animals make their way through the world. His models are much more sophisticated, but the goal is the same: to understand energy transfer between an animal and its environment and how that affects the organism's behavior, survival, and distribution. Humans can use clothing, heating, and air-conditioning to extend the limits of what they can do at extreme environmental conditions. But other animals are not so lucky. They can seek food and mates only when their bodies fall within a certain temperature range. They may have adaptations, such as changing the color of their skin, that can help, or they can move into the shade or sun depending on the time of day. Yet in the end, temperature still constrains most creatures, whether they are warm- or cold-blooded.

    To predict where and when animals will function, “the place to start is temperature,” says Raymond Huey, an evolutionary physiologist at the University of Washington, Seattle. It's “better than any other environmental factor.” Temperature constraints affect the survival of individual animals, specific populations, and even whole species. “There is a growing awareness of the valuable role that physiological knowledge can play in understanding organism-environment inter actions,” says Michael Kearney, a physiological ecologist at the University of Melbourne in Australia.

    Test case.

    This virtual sea turtle is helping computer modelers determine where oceans might become too warm for the real leatherbacks.


    Such knowledge has become in creasingly important given the threat of climate change. While some researchers compare historical and current records to assess how warming might affect the range of a species, modelers such as Porter make predictions in silico. “The models allow a direct connection to be made between what we measure about the physiology of an organism and climatic data,” Kearney says. “It's an exciting area, and it's a relevant area because of the focus and awareness of environmental change,” adds Huey.

    For every hour they work at the computer running a model, researchers may spend days in the field taking measurements to validate or refute their virtual animal. Early versions of animal models needed many simplifying assumptions on matters such as the shape of the animal and straightforward scenarios to make them computationally tractable. But researchers can now incorporate many more details, making simulations much more realistic and meaningful, says Michael Sears, an ecologist at Bryn Mawr College in Pennsylvania.

    The virtual animals represented by these models still have their skeptics. All models make assumptions, each of which can introduce inaccuracies that some argue add up to be significant. But more decision-makers are making use of them, says Donald DeAngelis, a U.S. Geological Survey ecologist at the University of Miami in Florida. “Models let us put the information that we have together in a rational, orderly way to make predictions about the future,” he says. “Without them, all we can do is guess.”

    Humble beginnings

    When Porter began experimenting with computer models, his goal was simply to predict the body temperature of a lizard of a given size, weight, and color in a particular environment. His first challenge was to convert local temperature, wind speed, and sunlight data into information relevant to the lizard itself—conditions on the ground, and even underground. For that, Porter and his colleagues developed a microclimate model and combined its results with lizard physiological and morphological data to predict the animal's temperature under particular conditions.


    Ecologist Michael Sears of Bryn Mawr College demonstrates a computer model that uses temperature, shading, and topography to predict the behavior of lizards as they try to maintain optimal body temperature in a desert environment.

    To see if this crude first model reflected reality, Porter built casts of real lizards using dental wax, plaster of Paris, and aluminum and painted them to reflect sunlight just like the real animals. He placed the casts outdoors with temperature sensors and found that they were within 2°C of what the virtual lizards in his model experienced. “Warren Porter and some of his colleagues were the first people to try to do modeling really looking at the balance of energy in individual organisms,” DeAngelis says. “It was a new approach at the time.”

    Through the years, Porter has refined and adapted his model to different animals and new situations. He gave the virtual lizards the ability to be active when their body temperature allowed it and incorporated food and water requirements to better determine how a lizard would fare under a given condition. To make the model more general, he came up with a version that had a virtual layer of insulation, akin to fur and feathers, thereby letting him study birds and mammals.

    At its core, his model incorporates three aspects of energy transfer. Based on the animal's size and color, it calculates the heat loss for a particular microclimate and, consequently, what temperatures the animal experiences. Other researchers have figured out the temperature range at which many species can be active, and the model uses that information to determine how much time an animal might spend eating and drinking. This determines how many calories the virtual animal takes in and burns and the amount of water it consumes and loses, a mix of numbers that adds up to its so-called mass balance. And finally, the model looks at what Porter calls momentum balance, the energy costs of moving.

    The models keep getting more sophisticated. In Porter's early work, for example, the bodies of lizards were treated as simple cylinders by the computer programs; now the simulations take into account the real shapes of organisms.

    His recent look at leatherback turtles offers further evidence of how far the field has come. As these 2.5-meter-long sea turtles swim, the exertion causes their overall body temperatures to rise, so the animals need to be in water cool enough to keep them from overheating. Porter has begun to determine where in the ocean these lumbering giants are likely to be found. He starts with off-the-shelf 3D modeling and computational fluid dynamics software programs that let him simulate a 3D virtual turtle swimming through water. That simulation enables him and his colleagues to calculate the drag on the animal, which helps them formulate the energy expended by the turtle and the excess heat produced. His model calculates heat loss in different ocean temperatures and from there, the simulation spits out where the seas are cool enough for the leatherbacks.

    Porter and his colleagues have applied his computer programs to many species: diving birds, tsetse flies, polar bears, whooping cranes, elk, an extinct Hawaiian honey-creeper, a rare viper in Taiwan, and tuatara, a living fossil reptile found in New Zealand. “We're in the position to design any kind of animal and put it in any place in the world and find out how much food and water it needs,” Porter says. The models “are extremely detailed and work remarkably well,” Huey notes.

    On the rocks.

    Plastic models of mussels provide temperature information important for simulations of how the bivalves fare at a particular site.


    Using Porter's research as a starting point, Melbourne's Kearney has recently broadened the scope of such modeling efforts. Working with Brian Helmuth of the University of South Carolina in Columbia, he has linked Porter's model to theories about how animals use energy and food and water for all aspects of their life history, including development, growth, and reproduction. “I can use the integrated models to understand climatic constraints on the entire life cycle and [on] population-level phenomena,” Kearney says.

    Helmuth studies intertidal organisms, in particular mussels and sea stars, with similar goals. “What we've been doing with terrestrial animals, he's doing with marine animals,” Porter says. For Helmuth, a big challenge has been ground-truthing the models. To do that, he's developed “robomussels”—plastic devices shaped and colored like mussels to handle heat the same way—with temperature sensors inside. He's planted them at 40 intertidal zones around the world.

    His goal is to find those places where mussels are being, or will be in the near future, pushed to their limits. And although there may not be much that people can do in the short term to stem rising temperatures globally, Helmuth says, “we may be able to ameliorate other stresses,” such as pollution or overfishing, that might push mussels at a particular location over the edge. He is now trying to determine just how fine-scale he must model wind speed, cloud cover, and other factors to get the model's predictions to reflect reality. Can remote-sensing data suffice, or are on-site weather stations necessary? “How do you get the local detail that you need without getting so mired in [it] that you don't see the broad pattern,” he wonders.

    Getting down to spatial details

    With his own biophysical models, Bryn Mawr's Sears has found that it's very important to look on the fine scale. Like Porter, he started out as a field biologist with a puzzle: Lizards living at lower elevations were smaller than lizards higher up, even though conventional wisdom held that the cooler climate at high elevations should retard physiological growth. Suspecting that the more desertlike environment lower down constrains the lizards' growth, he and Michael Angilletta Jr., a physiological ecologist at Arizona State University, Tempe, decided to determine how lizards might cope with the heat.

    Their simulations and subsequent field studies showed that the hot sun did limit lizard activity, but in a more complex way than researchers had assumed. The limitations imposed by heat depended significantly on the distribution of shade in the particular lizard's environment. “The pattern of [shade] variation has a huge impact on their ability to thermoregulate,” Huey says. “They've done a really nice simulation and analysis to show that.”

    Sears started by creating a realistic simulation of the lizard's desert habitat, which required a visit to sand dunes in central New Mexico to obtain fine-scale temperature measurements. He and his colleagues then wrote a computer program that could specify how hot each 0.5-meter-square spot would be at different times of the day, depending on where the sun was. It's a computationally intense simulation, taking nearly 24 hours to factor in all the shadowing for a 100-square-meter plot with a bumpy, complex landscape—the vegetation coverage incorporated into the model was provided by aerial photos. “They were the first to really factor in spatial [heterogeneity] on a small scale,” Huey says.

    Daily struggle.

    The Yarrow spiny lizard (top) must move around quite a bit to stay cool, according to simulations of how temperature changes throughout the day in its vegetation-covered landscape (bottom, left).


    Next, Sears plops a virtual lizard of a particular size into various versions of his landscape model. In some, there are big patches of shade, as if there are few big trees; in others there are many small patches, the equivalent of small bushes. He gives the virtual animal the goal of maintaining an optimum temperature for finding food. The lizard initially finds shade, but eventually has to move on to another location because of the shifting sunlight, for example. “What our models have done is focus on where those temperatures are available in space and whether animals can actually use them,” Angilletta explains.

    To see if their models were valid, Angilletta and Sears spent almost 2 summers in the Chihuahuan desert in New Mexico building fenced-in 400-square-meter plots, arrayed with different configurations of shade cloth. They then released about 80 lizards into these plots and carefully monitored the lizards' movements. Their data from these plots support what the models are predicting: Lots of small patches of shade and sun are better for the animals than a few big patches.

    Shade arrays.

    Large areas covered with different patterns of shade cloth, as seen in the aerial photo (left), helped researchers evaluate simulations showing the importance of diverse shading in hot environments.


    Knowing that heterogeneity of a habitat makes a difference can matter. Conservationists working to protect the dune sagebrush lizard are trying to decide where to set aside land and how to manage these conservation areas. Sears's modeling work shows that the threatened species should be able to be active 20% to 50% longer in complex habitats. “The more complex habitats are probably the ones you should focus on preserving,” he says.

    While Sears and other animal modelers are typically trying to simulate the current reality, when they tweak their computer programs to plug in temperature changes due to global warming, the situation can become dire for some species. “You're going to have a change in the number of places an animal can find its preferred temperature, but you are also going to have a change in where those are in space and how connected they are,” Angilletta explains. For example, lizards may not be as able to reach a preferred place because they would heat up too much as they travel from one to another.

    Angilletta and Sears next plan to add other aspects of lizard ecology—such as predators or rivals—to their models to see how that affects the animal's ability to keep its temperature right. And Angilletta is working on other modeling projects to come up with predictions for how an entire species can be affected by climate change. Through such modeling, “the biological consequences of environmental change are addressable, probably for the first time,” Huey says.

    That's a long way from simply explaining why a desert iguana changes color, but Porter says the underlying principles of the research are the same. “The computational biology is just a tool to understand what it is that makes animals work,” he concludes.