This Week in Science

Science  30 Apr 2010:
Vol. 328, Issue 5978, pp. 543
  1. Hotspots on Venus


    The surface of Venus shows clear signs of volcanism, but are there active volcanoes on Venus today? The answer to this question will bear on our understanding of the planet's climate evolution and interior dynamics. Using surface thermal emissivity data returned by the Venus Express spacecraft, Smrekar et al. (p. 605, published online 8 April) looked at three hotspots on Venus. These places were identified by analogy with terrestrial hotspots like Hawaii, which are believed to overlie mantle plumes and to be the most likely sites for current volcanic activity. Lava flows at the three hotspots have anomalously high thermal emissions when compared with their surroundings. Low emissivity is generally interpreted as the result of surface alteration by the corrosive atmosphere of Venus. High emissivity implies that not much alteration took place and thus that the hotspots must represent recently active volcanoes younger than 2.5 million years.

  2. Grassland Emergence

    The evolution of the C4 photosynthetic pathway from the ancestral C3 pathway in grasses led to the establishment of grasslands in warm climates during the Late Miocene (8 to 3 million years ago). This was a major event in plant evolutionary history, and their high rates of foliage production sustained high levels of herbivore consumption. The past decade has seen significant advances in understanding C4 grassland ecosystem ecology, and now a wealth of data on the geological history of these ecosystems has accumulated and the phylogeny of grasses is much better known. Edwards et al. (p. 587) review this multidisciplinary research area and attempt to synthesize emerging knowledge about the evolution of grass species within the context of plant and ecosystem ecology.

  3. Division Machinery Tagged

    An international consortium of labs has been testing the feasibility of large-scale screening for insights into the function of mammalian proteins by expressing a tagged version of proteins from bacterial artificial chromosomes harbored in mammalian cells. Depending on the tag used, Hutchins et al. (p. 593, published online 1 April) were able to monitor localization of tagged proteins by microscopy or to isolate interacting proteins and subsequently identify the binding partners by mass spectrometry. Applying the technology to proteins implicated in control of cell division revealed about 100 protein machines required for mitosis.

  4. Dusty Quasars

    Quasars are energetic sources thought to be fueled by matter accreting onto black holes a billion times more massive than the Sun. Some quasars are difficult to detect because of surrounding clouds of gas and dust, so much so that this population of objects has remained elusive. Based on a compilation of x-ray, optical, and mid-infrared data, Treister et al. (p. 600, published online 25 March; see the Perspective by Primack) show that the evolution of quasars across cosmic time occurs during mergers of gas-rich galaxies, with an obscured phase preceding an unobscured state by about 100 million years. Other objects have been detected in diverse wavebands, including ultraluminous infrared galaxies, which are known to be the product of similar gas-rich mergers of massive galaxies.

  5. Approaching Lactate Inorganically

    Conversion of biomass to value-added chemical compounds currently relies in large part on fermentation. For full-scale displacement of petroleum as the chemical industry's primary feedstock, alternative conversion technologies will be necessary. Holm et al. (p. 602) have found that Lewis acidic zeolite derivatives suspended in methanol can catalyze the selective conversion of glucose, fructose, and sucrose sugars to methyl lactate, a versatile synthetic intermediate for commercial products. The catalysts were easily separated from product mixtures and proved robust over six reaction and regeneration cycles.

  6. Riding the Monsoon

    Most air transport from the troposphere to the stratosphere occurs in the tropics, but additional transport may occur in areas of strong upward convection. Randel et al. (p. 611, published online 25 March) report satellite measurements of atmospheric hydrogen cyanide over the region where the Asian summer monsoon occurs, which indicate that air is transported from the surface to deep within the stratosphere. This mechanism represents a pathway for pollutants to enter the global stratosphere, where they might affect ozone chemistry, aerosol characteristics, and radiative properties.

  7. Pink for Me, Green for You


    Aphids come in different colors, a critical issue when fate is a question of pigmentation: Red aphids tend to be consumed by ladybugs and green ones by parasitic wasps. Aphid color is determined by carotenoids, the same group of chemicals that make flamingos pink. But unlike flamingos, which have to eat colored food to stay pink, aphids make their own pigment. Carotenoids are vital to animals, not only because of their decorative possibilities but also for their oxidation-protective qualities as visual pigments and immune-system modulators. On sifting through an aphid genome, Moran and Jarvik (p. 624; see the Perspective by Fukatsu) discovered that the machinery for producing carotenoids has been acquired by an ancestral aphid in a lateral transfer event from a fungus. Although a spontaneous yellow mutant aphid was found that still possesses the sequence for biosynthesis of the red carotenoid pigment torulene, the sequence was discovered to have a single point mutation that puts a stop to turning red.

  8. Learning to Work Together

    In group endeavors, there is often a tension between working for the greater good of the group as a whole versus working for one's own benefit. Sometimes these paths coincide and sometimes they do not; furthermore, the choices made by other group members can influence the calculation of which path to take. A pair of studies now approaches this challenge from experimental and theoretical points of view. In a forest or fishery, harvesting of wood or food needs to take into account the renewable character of the resource, as well as spatial heterogeneity. Janssen et al. (p. 613; see the Perspective by Putterman) show that communication among the group members is key, both to establishing a maintainable rate of harvesting, as well as enforcement via punishment of noncompliers. Boyd et al. (p. 617; see the Perspective by Putterman) develop a model showing that punishment, which is a costly activity, is most effectively levied when implemented with the approval of group members; that is, coordinated punishment works to the benefit of the whole, whereas individual actions do not.

  9. Biofilm Today, Gone Tomorrow


    Most bacteria can form complex, matrix-containing multicellular communities known as biofilms, which protect residents from environmental stresses such as antibiotic exposure. However, as biofilms age, nutrients become limiting and waste products accumulate, and biofim disassembly is triggered. Now Kolodkin-Gal et al. (p. 627) have found that d-amino acids found in conditioned medium from mature biofilms of Bacillus subtilis prevent biofilm formation and trigger existing biofilm disassembly.

  10. Light Structures

    Absorption of light by photosynthetic reaction centers causes structural changes and triggers a series of electron transfer reactions, resulting in a transmembrane potential difference that can be used to drive the subsequent chemistry. The initial electron transfer generates a charge-separated state that must be stabilized to prevent dissipation of energy through recombination. Wöhri et al. (p. 630) have used time-resolved Laue diffraction crystallography to observe light-induced conformational changes that occur within milliseconds of photooxidation of the dimer of bacteriochlorophyll molecules, known as the “special pair,” in the photosynthetic reaction center of Blastochloris viridis. Stabilization appears to occur because of the deprotonation of a conserved tyrosine residue that moves closer to the special pair.

  11. Frog Genome

    The African clawed frog Xenopus tropicalis is the first amphibian to have its genome sequenced. Hellsten et al. (p. 633, see the cover) present an analysis of a draft assembly of the genome. The genome of the frog, which is an important model system for developmental biology, encodes over 20,000 protein-coding genes, of which more than 1700 genes have identified human disease associations. Detailed comparison of the content of protein-coding genes with other tetrapods—human and chicken—reveals extensive shared synteny, occasionally spanning entire chromosomes.

  12. A Dip in the Carbon Pool

    Before the diversity of animal life exploded in the Cambrian, Earth's carbon cycle was apparently strongly altered by multiple glaciation events across the globe. Carbon isotope signatures from rocks in Australia measured by Swanson-Hysell et al. (p. 608) suggest that an organic carbon reservoir formed between two global glaciations, or “snowball Earth,” several hundred million years earlier than expected. Anoxic sulfate-limited waters, caused by increased river outputs from melting glaciers, may have prohibited bacterial respiration, allowing for the accumulation of organic carbon. As organic carbon levels dropped, CO2 was released, allowing the atmosphere to warm, preventing further glaciations, and permitting the eventual accumulation of oxygen in the oceans that led to the Cambrian explosion.

  13. The Wasps and the Bees

    Sex development in bees and wasps depends on whether or not they develop from a haploid unfertilized egg (resulting in males) or diploid fertilized egg (resulting in females). Although these ploidy-level developmental processes are conserved among bees and wasps, the mechanisms that direct development down a male or female pathway differ significantly. By examining the sex-determining genes in the parasitoid wasp Nasonia, Verhulst et al. (p. 620) have shown that a maternal messenger RNA (mRNA) is necessary to initiate the female pathway. The mRNA operates in combination with conserved maternal and paternal genes to produce females, which explains why females are diploids. In unfertilized eggs, maternal provisioning of the gene transcript is too low to initiate the female pathway.

  14. Runs in the Family

    The power to detect mutations involved in disease by genome sequencing is enhanced when combined with the ability to discover specific mutations that may have arisen between offspring and parents. Roach et al. (p. 636, published online 10 March) present the sequence of a family with two offspring affected with two genetic disorders: Miller syndrome and primary ciliary dyskinesia. Sequence analysis of the children and their parents not only showed that the intergenerational mutation rate was lower than anticipated but also revealed recombination sites and the occurrence of rare polymorphisms.

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