This Week in Science

Science  10 Dec 2004:
Vol. 306, Issue 5703, pp. 1857
  1. Brainy and Agile Birds

    CREDIT: EMERY AND CLAYTON

    Anecdotal evidence and human folklore have always ascribed a comparatively high level of intelligence to corvids—crows, rooks, jays, and ravens—and recent experiments on their cognitive abilities have begun to put this reputation on a factual basis. Emery and Clayton (p. 1903) review field studies and experimental studies which show that for a number of tasks that involve higher cognitive functions, corvids' abilities rival or excel those of apes. Corvids are amazingly skilled in three areas: Tool manufacture and use; mental time travel; and social cognition. In another area of convergent evolution, that of flight, our understanding of insect flight was greatly improved almost a decade ago with the discovery of leading-edge vortices on their wings. Technical difficulties of monitoring air flow around wing surfaces of flying birds to look for similar effects have now been overcome by using water instead of air as the moving fluid. Using models of wings of the common swift in a water tunnel, Videler et al. (p. 1960; see the Perspective by Müller and Lentink) show that leading-edge vortices can also generate lift for birds. In birds, the lift generated appears to be important for aerobatic prowess, rather than simply keeping airborne.

  2. Semiconductors in a Spin

    A current flow through a conductor in a magnetic field leads to a measurable voltage in the transverse direction (the Hall effect). Recent theoretical work has predicted the existence of an analogous effect for the spin in semiconductors, the spin Hall effect. Kato et al. (p. 1910, published online 11 November 2004; see the 12 November news story by Service, the cover, and the Perspective by Bauer) present experimental data confirming the accumulation of net spin on opposite sides of a GaAs sample. The ability to create and detect a spin current in a nonmagnetic material, without the need for an external magnetic field, may lead to applications in spin electronics.

  3. Large Shallow Quakes

    An estuary along the eastern coast of Japan shows evidence for multiple episodes of uplift during the past few hundred thousand years, but the cause of this uplift is poorly understood. Sawai et al. (p. 1918) found a tsunami deposit closely followed by a series of uplifted mudflats that formed in the 17th century. The large size of the tsunami along with the large amount of uplift indicate that a large magnitude, shallow earthquake occurred along the subducting plate boundary. The uplift was probably produced by transient creep along the subduction zone or mantle relaxation for tens of years after the event.

  4. Oscillatory Superconductivity

    CREDIT: GUO ET AL.

    When the thickness of films approach several monolayers, quantum size effects may result from the confinement of the electrons in the vertical direction. Theoretical work has predicted that quantum size effects should also appear in thin superconducting films as a well-defined oscillation of the transition temperature Tc. Guo et al. (p. 1915; see the Perspective by Chiang) produced uniform thin Pb films whose thickness could be controlled to within a single monolayer and observed the predicted oscillations in Tc.

  5. Recombination and Diversity

    DNA recombination may represent the driving force for sex in eukaryotes and a major source of adaptation and diversification in bacteria. The role of recombination in the third branch of life, Archaea, has not been clear. Papke et al. (p. 1928) analyze a population of haloarchaea in solar salterns near Alicante, Spain. The association of gene alleles is essentially arbitrary, which suggests that the saltern populations are likely to be recombining their DNA freely with each other. The high level of “linkage equilibrium” measured for haloarchaea is similar to levels seen in sexual eukaryotic populations.

  6. Which Way Out for Plasmodium Proteins?

    In mammals, malaria parasites live within red blood cells and decorate the host cell surface with immune evasive variant antigens encoded by the var genes. Erythrocytes lack a secretory machinery, and so the parasite must create one. Hiller et al. (p. 1934) and Marti et al. (p. 1930) now define motifs that route proteins into the red cell cytoplasm (see the Perspective by Przyborski and Lanzer). Without these signals, or if critical residues are mutated, the proteins are trapped within the parasitophorous vacuole.

  7. Genetic Blueprint of the Silkworm

    It is easy to see the differences between moths and flies, but what are the differences at the genetic level? Xia et al. (p. 1937) present a draft genome sequence for the silkworm moth, Bombyx mori. This lepidopteran diverged from the previously sequenced dipteran insects (fruit fly and mosquito) more than 280 million years ago. Domains can now be identified that are unique to insects or unique to the silkworm. The silkworm genome (more than 18,000 genes) is larger than that of Drosophila because of increases in gene number and size. As more sequence information is analyzed, it will be possible to correlate the dramatic morphological diversity that is seen among the insects with gene diversity.

  8. Learning from Experience in Parkinson's Disease

    Learning from experience means that positive feedback or reward is used to reinforce behaviors, and negative feedback is used to avoid such behavior. Dopaminergic pathways are thought to contribute to both kinds of feedback. Frank et al. (p. 1940, published online 4 November 2004) previously formulated a computational model which predicted that the loss of dopamine in patients with Parkinson's disease should make it more difficult for them to learn from positive reinforcement but, counterintuitively, easier to learn from negative feedback. Conversely, patients on medication that increases dopamine levels should display the opposite pattern of learning efficiency. Testing patients on two kinds of cognitive tasks, on and off medication, confirmed these predictions and may provide an explanation for the sometimes puzzling effects on learning during treatment of patients with Parkinson's disease.

  9. Organic Aerosols Overstay

    CREDIT: MARIA ET AL.

    Aerosols affect climate by their influence on how much solar radiation is reflected into space or absorbed in the atmosphere. The effects occur both directly as well as indirectly (by modifying cloud distributions and properties). The effects of chemical reactions on the properties of aerosols have been difficult to characterize. Maria et al. (p. 1921) calculated the oxidation rates of the organic molecules in carbonaceous aerosols, which comprise a large fraction of the total atmospheric aerosol burden. They measured which organic functional groups occur in individual particles and combined those data with insights into the microphysical processes that direct particle growth. With this method, they conclude that conversion rates are a factor of 3 lower than those typically used in climate models, thus leading to longer aerosol lifetimes and changes in their overall effects on cooling and warming.

  10. Cocaine Signals Never Disappoint

    The temporal difference reinforcement learning (TDRL) model provides a computational framework for describing how future rewards are valued, how current choices are made, and how differences between what is received and what is expected are fed back into updated calculations of future rewards. In TDRL, the difference signal between receipt and expectation is carried by neurons that use the transmitter dopamine. Redish (p. 1944; see the Perspective by Ahmed) applies this model and develops an explanation, in neural computational terms, for some aspects of behavior in the context of addictive substances. The key point is that cocaine induces, via pharmacologic pathways, a dopamine signal that does not accurately reflect or respond to the difference in actual and expected reward; cocaine is always valued as being more rewarding than originally thought.

  11. Controlling Ovulation

    In the mammalian ovary, oocytes are maintained in meiotic arrest until the female ovulation cycle directs meiosis to resume just prior to ovulation. A Gs-linked receptor in the mouse oocyte membrane acts as a regulator of the transition between meiotic prophase and metaphase. Mehlmann et al. (p. 1947) now identify GPR3 as the oocyte receptor required for the maintenance of prophase arrest.

  12. Estrogen Receptors Act in Atherosclerosis

    Men experience a more rapid progression of atherosclerosis, but the basis for this gender difference has not been clear. The prostacyclin PGI2 prevents many processes associated with the formation of atherosclerotic lesions, and the atheroprotective effect of estrogen in women may be via stimulation of PGI2 production. Egan et al. (p. 1954, published online 18 November 2004; see the 19 November news story by Couzin) now show in a mouse model of atherosclerosis that estrogen acts through the estrogen receptor subtype to generate PGI2 through cyclooxygenase 2 (COX-2). Female mice lacking a receptor for PGI2 developed atherosclerosis as rapidly as male mice and had poor response to estrogen therapy. This mechanism may be important in assessing the effects of hormone replacement therapy and selective COX-2 inhibitors.

  13. Sharpening Metal Interfaces

    When metal multilayers are fabricated by depositing atoms for the vapor phase, diffuse interfaces usually form where the two atom types intermix. If the two species are fully miscible, the interfaces would broaden with heat treatment because of the interdiffusion of the atoms in the adjoining layers. Erdélyi et al. (p. 1913) show that this is not what happens for the molybdenum-vanadium system—as the temperature is increased, the interfaces become sharper. Theoretical calculations show that in this case, diffusion has a nonlinear dependence on the local concentration and leads to segregation. This sharpening may be of use in fabricating mirrors for x-ray or neutrons that are based on multilayer metal structures.

  14. Tracking Langmuir Supercells

    Langmuir circulations are parallel, counterrotating vortices in the surface layers of lakes and oceans caused by wind and waves. They transport water both upward and downward and are important for understanding vertical mixing. Most of the observational and theoretical work on oceanic Langmuir circulations have been done for cases where the water depth is greater than that of their penetration, and little attention has been given to cases where the Langmuir cells extend to the sea floor to form supercells. Gargett et al. (p. 1925) report detailed observations of Langmuir circulations in shallow waters (15 meters) off the New Jersey shore, an environment typical of vast coastal shelf areas. Langmuir supercells are an important mechanism for sediment resuspension and transport there, and they may also have significant effects on shallow- shelf benthic ecosystems.

  15. Unraveling Werner Syndrome

    Werner syndrome (WS) patients suffer many symptoms of premature aging, including wrinkled skin, graying hair and hair loss, osteoporosis, heart disease, and cataracts. Cells from WS patients enter senescence prematurely, show increased rates of genome instability, and rapidly lose their telomeres, the protective ends of their chromosomes. The WRN helicase, mutated in WS, is involved in the maintenance of the telomeres, possibly through the untangling of “knotty” (G-quadruplex) DNA. Crabbe et al. (p. 1951) show that the WRN helicase is associated with telomeric DNA during S-phase of the cell cycle. Loss of WRN helicase activity leads to the loss of telomeres from single sister chromatids, and only telomeres replicated by lagging-strand DNA synthesis are affected.

  16. Polymorphisms Drive Plant Pathogen Resistance

    Plants defend against certain pathogens in a gene-for-gene manner, with specific defense proteins aligned against specific pathogen strains. As pathogens evolve, so must defenses. The greatest variability from the plant's side lies within a domain of its defensive response protein that is implicated in protein-protein interactions. Rapidly diverging defensive alleles are now shown by Allen et al. (p. 1957) to be faced off against rapidly diverging alleles in the invader's pathogenicity effectors. Both the plant's response gene and the pathogen's effector gene show genetic polymorphism driven by balancing selection.