This Week in Science

Science  12 Nov 2004:
Vol. 306, Issue 5699, pp. 1097
  1. Seismic Ebb and Flow


    Tides caused by the gravitational pull of the Sun and the Moon can create a small amount of localized stress in the crust, yet there has been no clear correlation between tides and earthquakes. Cochran et al. (p. 1164, published online 21 October 2004) have found that some shallow thrust-fault earthquakes have been triggered by strong tides. Quantifying the amount of stress needed to tidally trigger these events will provide more understanding of earthquake nucleation.

  2. Spin Triplets and Quantum Criticality in Strontium Ruthenates

    Initial studies of the superconductor strontium ruthenate indicated that the electron pairing proceeded through the spin-parallel triplet rather than the typical antiparallel singlet. Confirmation of this exotic form of superconducting behavior has, however, remained elusive. Nelson et al. (p. 1151; see the Perspective by Rice) performed phase-sensitive experiments across junctions formed by strontium ruthenate that provide conclusive evidence for the pairing occurring through the spin triplet. Quantum phase transitions are promoted at zero temperature by some external parameter other than temperature, and it has been suggested that such conditions should lead to exotic phases. In the vicinity of a quantum critical point in strontium ruthenate tuned by magnetic fields, Grigera et al. (p. 1154) find experimental evidence for the formation of a new phase driven by an instability in the Fermi surface. This class of phase transition was initially described theoretically nearly half a century ago.

  3. Single-Crystal Spines

    The spines of sea urchins are composed of large, highly patterned single crystals of calcium carbonate. By studying the regeneration of the spine, Politi et al. (p. 1161) provide evidence that these convoluted crystalline structures develop through the deposition of an amorphous precursor phase. Through a slow transformation, the highly patterned amorphous structure is converted into a single crystal of calcite that preserves the initially deposited shape.

  4. Staying Mixed


    The ratio of 14C to 12C in the atmosphere is controlled mainly by the production of 14C, which is a function of cosmic-ray flux to Earth, and the redistribution of CO2 between the atmosphere and the deep ocean. The deep ocean contains “old” carbon in which the 14C has had time to decay substantially (14C has a half-life of 5370 years), so if its flux back into the atmosphere is inhibited, the 14C/12C ratio of the atmosphere will increase. Elevated atmospheric 14C/12C ratios during the last glacial maximum might have resulted from a lower deep-sea ventilation rate and a reduction in shallow marine carbonate deposition. Broecker et al. (p. 1169; see the Perspective by Adkins and Pasquero) examined the 14C/12C of shallow and deep ocean foraminifera and found that the radiocarbon age of water at 2 kilometers' depth in the Western Equatorial Pacific was no greater than it is today, which makes it unlikely that reduced ocean mixing caused the observed variations in 14C/12C.

  5. Curbing Poverty and Promoting Biodiversity

    Human poverty and dwindling biodiversity frequently coincide, especially in developing countries. In recent years, a view has been developing that conservation and poverty reduction should be tackled together. Adams et al. (p. 1146) review the current challenges at the interface between policies for biodiversity conservation and poverty reduction.

  6. Virulence in Context

    Tracheal cytotoxin (TCT) is a bacterial virulence factor in whooping cough (and other infections) that triggers leukocyte infiltration and strips airways of ciliated epithelium. However, not all host-bacterial encounters are negative. In the relationship between the glow-in-the dark squid Euprymna scolopes and its luminescent bacterial symbiont Vibrio fischeri, Koropatnick et al. (p. 1186; see the cover) have discovered that the same toxin plays a benign role. In this association, TCT still initiates apoptosis of ciliated cells and host cell infiltration. However, these cellular responses are triggered when juvenile squid first encounter V. fischeri and constitute a normal developmental stage in the generation of the specialized light organ that allows it to accommodate the incoming symbiont.

  7. Mitochondria--Culprits Again in Metabolic Disease

    Hypertension and high levels of cholesterol are often associated with one another in the general population, notably in individuals who have “metabolic syndrome,” a constellation of disorders that also includes insulin resistance and diabetes. Studying a large family with a high prevalence of hypertension, elevated cholesterol, and low serum levels of magnesium, Wilson et al. (p. 1190, published online 21 October 2004; see the 22 October news story by Marx) find that the causative mutation lies in an isoleucine transfer RNA gene encoded by the mitochondrial genome. Thus, the clustering of these three metabolic traits may arise from a single underlying factor—mitochondrial dysfunction. Coupled with previous evidence implicating mitochondrial dysfunction in insulin resistance and type 2 diabetes, this discovery raises the intriguing possibility that mitochondria play a key role in most components of metabolic syndrome, a disorder that may affect up to 25% of adults in the United States.

  8. Dwindling Fish Supply Promotes Bushmeat Consumption

    In many tropical countries, fish and terrestrial wildlife are the primary and secondary sources of animal protein for humans. Brashares et al. (p. 1180) use 30 years of data from West Africa to show a direct link between marine harvests and human consumption of terrestrial wildlife at a regional scale. Rates of wildlife decline are also related to fluctuations in bushmeat hunting and fish supply. An examination of prices and supply and demand data for fish and bushmeat from 12 local markets revealed the mechanisms linking marine productivity and terrestrial conservation. The activities of the large and heavily subsidized European Union foreign fleet may contribute to the declines in West Africa's fish supply and thereby contribute to associated increases in consumption of terrestrial wildlife.

  9. Reversible Male Immunocontraceptive

    Although reliable birth control methods for females have been around for decades, the choices available for men are few. O'Rand et al. (p. 1189; see the news story by Couzin) now report a method of nonhuman primate contraception that is based on the immune response to an epididymal protein, Eppin. This nonhormonal method is effective in monkeys that show high anti-Eppin titer, and the majority of animals that showed successful contraception were able to revert back to normal fertility.

  10. Going, Going, Gone


    Two major themes in ecological research are the dynamics of biodiversity loss in ecosystems, especially with respect to the effects of invasive species, and the relation between biodiversity (in the form of species richness) and the functioning of ecosystems (see the Perspective by Raffaelli). Zavaleta and Hulvey (p. 1175) provide a bridge between these two areas by testing how an observed sequence of species losses influenced ecosystem functioning. Species were lost in a particular sequence from grassland patches involving the rapid and early loss of unique functional groups. Losses, even of rare species, had strong effects on resource uptake and on the ability of the ecosystem to resist invasion by alien species. Using data from marine benthic invertebrate species, Solan et al. (p. 1177) model how the loss of biodiversity will impact ocean sediment bioturbation, the disturbance of sediment layers by biological activity which affects the fluxes of energy and matter that sustain marine ecosystems. Loss of biodiversity will reduce the depth of oxygenated sediments in ocean benthic habitats and likely alter fluxes of energy and matter on a global scale. Because the risk of extinction is generally correlated to the biological traits of species that influence bioturbation, the consequences of biodiversity loss depend on the order in which species go extinct and on the ultimate cause of the extinction.

  11. Illuminating Drug Discovery

    In drug discovery, profiling technologies are important for measuring drug actions both on the desired target and on other targets. High-throughput methods such as transcriptional and proteomic profiling provide data on the responses of populations of cells normally at single drug concentrations. Perlman et al. (p. 1194) describe a method for high-throughput cytological profiling that combines automated microscopy, image analysis, and statistical analysis. Using multiple fluorescent probes that cover a range of cell biological functions, they profiled the dose-dependent effects of 100 drugs on cultured mammalian cells. They succeeded in categorizing drugs of known mechanism and suggested targets for drugs of uncertain mechanism.

  12. Magma Tracers

    Analyses by Berlo et al. (p. 1167, published online 14 October 2004) of water and lithium concentrations in melt inclusions and concentrations of 210Pb in crystals from the volcanic rocks erupted from Mount St. Helens right before the catastrophic eruption of May 1980 and 6 years afterward provide information about the movement and degassing of magma. The data suggest that there is a deeper magma reservoir where magma stalls and degasses before rising to the shallow reservoir. These new chemical tracers may be useful for predicting new eruptions.

  13. Skirting the Transition State

    The general consensus in chemical kinetic theory is that reactions proceed along a single trajectory through a transition state, often likened to a mountain pass, and adding more energy to the system simply sends the molecules along this pathway more rapidly. Townsend et al. (p. 1158, published online 21 October 2004) have combined precise product energy measurements with theoretical modeling to show that formaldehyde (CH2O) can decompose to the same products, H2 and CO, along two very different paths. The dominant pathway proceeds through a transition state with relatively little motion of the H atoms. The alternate pathway never accesses this lowest energy transition geometry. Instead, one H atom nearly detaches itself from the molecule before binding the second H atom to form H2.

  14. Poor Man's Tree of Life

    Although DNA sequences are being accumulated at an ever-increasing rate, producing the “Tree of Life”—the family tree of all of the species on Earth—is complicated by the presently piecemeal nature of much sequence data. Driskell et al. (p. 1172; see the Perspective by Crandall and Buhay) used a bioinformatic approach to sample existing databases and create very large data sets with broad representation across the three domains of life. Even though many of the sampled genes were not sequenced for all species in the data set, creating very “sparse” gene matrices, useful phylogenetic information could be extracted that provide an important supplement to expensive sequencing initiatives.

  15. Reactive Oxygen Death Program

    Reactive oxygen species (ROS) are closely associated in plants and animals with disease, stress, and cell death. Wagner et al. now (p. 1183) show in the plant Arabidopsis thaliana that stress reactions formerly attributed to physico-chemical damage caused by one of these ROS, singlet oxygen, is the result of an actively pursued genetic program that requires a chloroplast protein, EXECUTER1. Inactivation of the EXECUTER1 gene was sufficient to protect plants from the damage normally induced by singlet oxygen.