This Week in Science

Science  03 Jan 2003:
Vol. 299, Issue 5603, pp. 13
  1. Subsurface Life

    The mission of the ocean drilling program (ODP) is to investigate the history of the ocean basins and the overall nature of the crust beneath the ocean floor. Cowen et al. (p. 120) have used a fluid sampling device in an ODP hole to investigate the sub-sea-floor habitat. The fluids are distinct from seawater and show evidence of water-rock reaction, as well as indirect evidence for biological activity—extremely elevated ammonia and decreased sulfate. The DNA isolated from the fluids revealed a subsurface ecosystem of diverse microorganisms (both bacteria and archaea) that are phylogenetically related to sulfate reducers and ammonia generators. The organic compounds discovered appear to be a distinctive part of the subsurface, rather than derived from surrounding sediments, and could be part of the organic geochemical budget that supports heterotrophic microorganisms. This subsurface ecosystem appears to be distinct from the communities found around black smoker vent systems.

  2. Flame-Triggered Supernova

    Type Ia supernovae are the result of a runaway thermonuclear explosion of a white dwarf. Gamezo et al. (p. 77; see the Perspective by Branch) developed a three-dimensional model of the initiation of an explosion by the heterogeneous expansion of a thermonuclear flame. The model accounts for the total kinetic energy released by a typical type Ia supernovae and indicates that the flame must trigger the detonation in the center of the destabilized white dwarf.

  3. Melting Away

    A growing body of evidence suggests that deglaciation in the West Antarctic Ice Sheet may still be evolving from the last glacial maximum. Stone et al. (p. 99; see the Perspective by Ackert) present surface exposure age data which show that there has been extensive deglaciation in the West Antarctic during the past 10,000 years. The West Antarctic Ice Sheet has thinned by more than 700 meters during this period, mostly in the last few thousand years. These findings support the idea that deglaciation in West Antarctica lagged the disappearance of the Northern Hemisphere ice sheets by millennia, and that the Antarctic has supplied at least some of the meltwater needed to explain sea-level changes during the past 7000 years.

  4. Long-Lived Interactions

    Subduction is an efficient method to transport larger ions that prefer to reside in Earth's crust, such as potassium and barium (Ba), into the mantle, where higher pressures and temperatures lead to chemical reactions and structural transformations of mineral phases. Catlos and Sorensen (p. 92) have measured the 40Ar-39Ar ages of distinct Ba-enriched regions of mica grains from two former subduction zones to estimate the temporal extent of fluid-rock reactions. The results suggest that fluid-rock reactions occurred in these subduction zones over time scales of 25 to 60 million years. Thus, the microscopic changes in the minerals can be used to trace the megascopic changes in the crust and mantle over long time periods.

  5. Delineating Higher Diamondoids

    The closing of rings and cages is always a challenge in organic synthesis, and the carbon-carbon lattices that make up diamonds are particularly difficult because of their size and symmetry. However, such compounds occur in petroleum, and are hardly curiosities—the amine derivative of the simplest of these compounds, adamantane, a tricyclic decane, has antiviral properties. Although adamantane was synthesized long ago, each higher adamantane, or “diamondoid,” has proven to be yet a more difficult synthetic target. Dahl et al. (p. 96; see the Perspective by Marchand) have now gone back to the source and separated pure fractions of more than 20 higher diamondoids, which contain up to 11 adamantane units. They also determined crystal structures for several of these compounds, including [121312] heptamantane.

  6. Pairing Up in Cuprates

    The maximum magnetic field at which Cooper pairing still occurs in type-II superconductors provides important information about their pairing strength and coherence length. Wang et al. (p. 86) present upper critical field studies of two bismuth-based families of the high-temperature superconductors that reveal an emerging picture in which the onset of superconductivity leads to a tradeoff between decreasing pairing strength and increasing superfluid density as the hole concentration increases.

  7. Orangutan Culture

    The possession of culture, in the form of regional differences in socially transmitted behavior, has been shown to exist in only one nonhuman animal, the chimpanzee. Van Schaik et al. (p. 102, see the news story by Vogel) now demonstrate cultural variation in orangutans based on a study of six wild populations in Borneo and Sumatra. Behaviors involving tool use, such as the use of leaves as napkins or sticks for scratching, showed geographical differences, with patterns that would be expected if these variants were socially transmitted. The authors conclude that human-like cultures date to at least 14 million years (the time at which ancestors of chimps and orangs diverged), which is much older than had been assumed.

  8. There's No Place Like Home

    Most marine fish produce larvae that must spend days, weeks, or even months developing in the water column. How far do they travel from home during this drifting stage? Taylor and Hellberg (p. 107, see the Perspective by Palumbi and Warner) combine direct measures of larval duration of Caribbean coral reef fishes with genetic estimates of population differentiation to show that populations of marine organisms can remain demographically closed for tens of thousands of generations, despite lengthy pelagic larval duration. Their data further suggest that assortative mating may enhance genetic differentiation of differently colored populations, which may explain in part the high diversity of brightly colored fishes found on coral reefs.

  9. Attention and Activity

    Visual attention, the ability to select one portion of the visual world around us for further processing, is important for perception and sometimes even for survival. In an electrophysiological study, Bisley and Goldberg (p. 81; see the Perspective by Yantis) found that the activity of neurons in an area of the monkey's brain (the lateral intraparietal area, or LIP) was correlated with the animal's attention during a discrimination task. The ensemble activity of neurons in the LIP, rather than the firing pattern of a single nerve cell, best described the spatial locus of a monkey's attention.

  10. Sticking Up for One Another

    A “green-beard” trait is one that would be readily recognized by fellow organisms bearing the allele and that gives rise to preferential treatment, regardless of the relatedness of the individuals concerned, that then favors this allele over others. Single genes that evolve such altruism have proved elusive. Queller et al. (p. 105; see the Perspective by Crespi and Springer) have now found an example of a single gene acting as a greenbeard trait in the slime mold Dictyostelium discoideum. The contact site A gene encodes a cell membrane protein (gp80) involved in cellular adhesion. When slime molds aggregate to form a fruiting body, “homophilic” recognition by cells that possess the wild-type gp80, is enhanced. That is, wild-type cells with the gp80 protein show preferential aggregation with each other.

  11. Mother Nose Best

    Changes in the numbers of olfactory neurons or in neuroblast migration to the olfactory bulb can affect abilities to discriminate odors or establish new odor-related memories. Studying female mice, Shingo et al. (p. 117; see the news story by Barinaga) show that the hormone prolactin induces increased production of olfactory cell precursors. The prolactin-induced changes were apparent during pregnancy and also just after mating. Odor discrimination contributes to recognition of mates and offspring.

  12. A Signal for Remodeling

    In eukaryotes, DNA is wrapped around nucleosomes to form a chromatin structure that is molded by adenosine triphosphate-dependent chromatin remodeling complexes in order to facilitate access by transcription factors. Shen et al. (p. 112) and Steger et al. (p. 114) both show that chromatin remodeling complexes can be regulated by small molecules known as inositol polyphosphates, providing a link between second-messenger signaling and nuclear activities.

  13. Complex Plastic Flow

    Understanding how dislocations nucleate and grow in plastic flow is important for material science, particularly metal fatigue, and for Earth science, particularly earthquake processes. Weiss and Marsan (p. 89) have mapped dislocations in single ice crystals under viscoplastic flow in three dimensions. Their experiments show that the dislocations have a fractal pattern and the dislocations can be correlated in space and time. Thus, they confirm that plastic flow is complex, heterogeneous, and intermittent, and can occur with a distinctive avalanche of dislocations.

  14. Long-Distance Legume Signaling

    Plant meristems serve as repositories of stem cells, on call to contribute to the development of a variety of organs and tissues. One type of meristem forms in the roots of legumes, where, upon interaction with nodulation signals from bacteria in the soil, it gives rise to nitrogen-fixing symbiotic nodules. Searle et al. (p. 109) now find that cell proliferation in these primordia of soybean is regulated by a receptor-like protein kinase, GmNARK, that is expressed in the plant's leaves. GmNARK resembles the Arabidopsis CLAVATA1(CLV1) protein that regulates cell proliferation in shoot apical meristems and affects shoot and floral development. An interesting divergence in the signaling system that these two proteins represent is that CLV1 acts over the short distances within the shoot apical meristem, whereas GmNARK acts from leaf to root. Soybean also has another gene that resembles CLV1, GmCLV1A, that functions within the shoot apical meristem in seemingly the same way as CLV1.

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