This Week in Science

Science  03 Feb 2012:
Vol. 335, Issue 6068, pp. 501
  1. A Drop in the Ocean


    The concentration of atmospheric CO2 rose by ∼80 parts per million (ppm), from ∼190 to 270 ppm, during the last deglaciation. It is widely believed that the primary source of that CO2 was the deep Southern Ocean. Burke and Robinson (p. 557, published online 15 December) present a 25,000-year-long record of the radiocarbon content of deep-sea corals collected from the Southern Ocean, which shows evidence of the 14C-depletion that must have accompanied CO2 sequestration. 14C depletion and ocean stratification ended between 15,000 and 14,000 years ago, in a manner consistent with the transfer of large amounts of CO2 from the deep Southern Ocean to the atmosphere. The observed 14C drop can explain the atmospheric CO2 rise between 17,500 and 14,500 years ago, adding support to the existing model of deglacial CO2 dynamics.

  2. Monitoring Meiosis

    During meiosis, or in yeast sporulation, haploid cells are generated from diploid cells. Brar et al. (p. 552, published online 22 December) performed a detailed analysis of messenger RNA (mRNA) abundance and protein synthesis over the course of sporulation. The production of most proteins was tightly regulated both at the mRNA level and by translational control. An unexpected complexity was observed as the cell passed through this key developmental transition, including increases in noncanonical translation from upstream regions of known RNA transcripts, which appear to be important in translational control.

  3. Nailing Down the Superfluid Transition

    A gas of fermions, the class of particle that protons, neutrons, and electrons belong to, can be found in contexts as different as neutron stars and a block of metal. When the interaction between fermions is on the brink of forming fermion pairs, the thermodynamics of the gas become dependent only on the gas temperature and density. Ku et al. (p. 563, published online 12 January; see the Perspective by Zwerger) measured this universal thermodynamics with high precision in an ultracold Fermi gas, observing the predicted transition into a superfluid state through the characteristic lambda-shaped transition in the gas's specific heat.

  4. Probing Pulsar Rotation

    Pulsars are strongly magnetized, rapidly rotating neutron stars. Those with periods of the order of milliseconds obtain their fast spin by accreting mass from a companion star in a binary system. Tauris (p. 561) combined numerical stellar evolution calculations with a model of how accretion torques act on a neutron star. During the late accretion phase of millisecond pulsars, the termination stage of mass transfer results in a loss of more than 50% of their rotational energy. This effect may explain the observed pulsar spin distributions.

  5. Monsoon Forcing

    Dansgaard/Oeschger (D/O) events—the sudden, millennial-scale periods of warmth that punctuate the cold climate of the Last Glacial period, and Heinrich events—cold intervals characterized by tremendous discharges of icebergs into the North Atlantic, have been observed at many locations in the Northern Hemisphere but not extensively in the Southern Hemisphere. Kanner et al. (p. 570, published online 12 January; see the Perspective by Rodbell) present a stable isotope record from the central Peruvian Andes, which represents a record of the South American Summer Monsoon from 50,000 to 16,000 years ago and which contains the signals of D/O and Heinrich events. The Southern Hemisphere monsoon displayed an antiphase relationship to Northern Hemisphere monsoon intensity at the millennial scale, and Antarctic millennial-scale climate fluctuations influenced the South American Summer Monsoon.

  6. An Iron Hand for Silicon


    Carbon-silicon bonds are integral to the structure of the silicone materials widely used in adhesives, cosmetics, and numerous other industrial and consumer products. Generally, platinum-based catalysts have performed best in the hydrosilylation reactions that form these bonds, but the expense of the precious metal and, in some cases, by-product formation have motivated a search for alternatives. Tondreau et al. (p. 567) now show that a class of iron compounds readily catalyzes hydrosilylation of certain commercially important substrates with rates and selectivities comparable to, or even exceeding, those associated with platinum.

  7. Girl Power

    The potential of affirmative action policies to reduce overall outcomes because of lower individual performance has been discussed widely and at length. But do quotas or preferential treatment of applicants alter the pool of candidates? Balafoutas and Sutter (p. 579; see the Perspective by Villeval) used an existing laboratory-based task to assess the change in composition of winning candidates and the overall outcome as a function of three affirmative action policies. Policies designed to encourage more women to enter a competitive environment served to recruit enough high-performing individuals to ensure that the efficiency in performing the task was preserved. Beaman et al. (p. 582, published online 12 January) examined the effects of a constitutionally mandated reservation of village-council and council-leader positions for women in West Bengal after two election cycles (1998 and 2003). The program appeared to narrow the gender gap in aspirations of parents for their children and of children for themselves; in addition, teenage girls spent more time in school and less on household chores. Beliefs and attitudes changed only after the second set of elections—that is, after a longer exposure to female role models—complementing the more rapid policy changes instituted by women council leaders after the first round of elections.

  8. Mystery of an Unextreme Microbe

    Metagenomics has given us glimpses into the huge diversity of microorganisms that are the engines of Earth's elemental cycling. These kinds of surveys can supply a good idea of the dominant organisms in ecosystems, but, because the majority of environmental microbes are difficult to culture and the most abundant organisms swamp metagenomes, it is difficult to discern the functional significance of other contributors. Iverson et al. (p. 587) sampled the Puget Sound and developed methods to reconstruct individual genomes from metagenomes, which allowed closure of a genome from the enigmatic marine group II Euryarchaeota. This Archaean is evidently motile, shows signs of extensive gene-swapping with bacteria, and offers some hints to the origin of proteorhodopsin—a molecule that some marine bacteria use to harvest energy from sunlight.

  9. Heat or Acid?

    The question of how tropical coral reefs will respond to increasing atmospheric greenhouse gas concentrations and concomitant climate change is widely debated. Model predictions and laboratory experiments suggest that decreasing carbonate saturation and decreasing pH may reduce calcification in carbonate-depositing organisms, including corals, yet field data are sparse, and recent declines in coral growth rates have been variously attributed to thermal stress or ocean acidification. Cooper et al. (p. 593) demonstrate that there has been no large-scale decline in calcification rates of massive Porites on coral reefs along the Indian Ocean coast of Western Australia. Instead, coral growth has increased significantly in the past 110 years, particularly at high latitudes. Thus, coral calcification appears to increase as ocean waters warm, but—at excessive temperatures—coral bleaching and reduced ocean carbonate saturation may lead to growth declines as observed on the Great Barrier Reef.

  10. Immune Sentinels


    A classic paradigm in immunology holds that the immune response occurs in two waves: Rapidly responding cells of the innate immune system help to contain the invading pathogen and alert lymphocytes. These cells of the adaptive immune system then help to clear the infection and go on to form long-lasting memory. However, some specialized populations of lymphocytes can also respond quickly to an infection and carry out functions that overlap with the innate immune system. Now, Rauch et al. (p. 597, published online 12 January) describe one such cell type—innate response activator (IRA) B cells. IRA B cells recognize bacterial liposaccharide through Toll-like receptor 4 and, in response, produce the cytokine GM-CSF, which activates other innate immune cells. Deletion of IRA B cells in mice impaired their ability to clear a bacterial infection and promoted septic shock.

  11. Nature or Drug Abuse?

    There are significant structural changes in striatal and prefrontal brain regions of stimulant drugdependent individuals. However, it is not clear if these brain abnormalities predate drug-taking, rendering individuals vulnerable for the development of dependence, or if these changes are the effect of many years of drug use. Ersche et al. (p. 601; see the Perpective by Volkow and Baler) investigated brain abnormalities in both drug-dependent individuals and in their biological siblings who have never taken drugs of abuse and compared them with matched healthy volunteers. The brain abnormalities in the sibling pairs were associated with significant impairments in the regulation of behavior; an ability known to be compromised in drug dependence. Because these neural changes were observed in family members who do not take drugs, the changes are likely to represent neurological markers of vulnerability to addiction rather than consequences of chronic drug abuse.

  12. Natural Resistance

    Avermectins are the most widely used class of anthelmintic drugs, both as pesticides and as treatments for nematode-borne diseases, with the evolution of resistance presenting a major global health and agricultural problem. Ghosh et al. (p. 574; see the Perspective by Wolstenholme) observed resistance to avermectin in the model nematode Caenorhabditis elegans that varies among isolates. This resistance is caused by a naturally occurring four–amino acid deletion in the ligand-binding domain of a glutamate-gated chloride channel. This variant also conferred resistance to the avermectin-producing ubiquitous soil bacterium, Streptomyces zitilis. Many nematodes spend at least part of their life cycle in soil, which may explain avermectin resistance among nematode species.

  13. Lineage Identity

    Segregation of endoderm and mesoderm lineages is a fundamental event in early embryogenesis. Using sea urchin embryos, Sethi et al. (p. 590) found that Notch and canonical Wnt pathways crosstalk progressively partitions the endomesoderm to discrete endoderm and mesoderm fates. This three-step signaling exchange demonstrates how the timing of signaling crosstalk is regulated in vivo through temporally and spatially staggered genetic circuits that intersect only at specific developmental stages.