This Week in Science

Science  04 May 2012:
Vol. 336, Issue 6081, pp. 517
  1. Hooking Up in Water Striders


    The male water strider Rheumatobates rileyi has an extensively modified antenna that is used for forced copulations with females. Khila et al. (p. 585) describe several microscopic antenna attributes that make the antenna fit perfectly with the female head when the male grasps the female. The features depend upon the expression of the gene distal-less (dll) during antenna development. Reducing the expression of dll compromised male grasping traits, while female antennae were unaffected.

  2. Giant Spin Hall

    One of the primary challenges in the field of spin-electronics, which exploits the electron's spin rather than its charge, is to create strong currents of electrons with polarized spins. One way to do this is to use a ferromagnet as a polarizer, a principle used in magnetic tunnel junctions; however, these devices suffer from reliability problems. An alternative is the spin Hall effect, where running a charge current through a material generates a spin current in the transverse direction, but the efficiency of this process tends to be small. Liu et al. (p. 555) now show that the spin Hall effect in Tantalum in its high-resistance β phase generates spin currents strong enough to induce switching of the magnetization of an adjacent ferromagnet; at the same time, Ta does not cause energy dissipation in the ferromagnet. These properties allowed efficient and reliable operation of a prototype three-terminal device.

  3. Uneven Gap

    Electron pairs that are responsible for the phenomenon of superconductivity can only be broken by investing a finite amount of energy, called the energy gap. The size of the gap may depend on the position on the Fermi surface; in cuprates, the gap completely disappears at certain points. What happens in the pnictide superconductors is still a subject of debate, not least because there appear to be differences between the different pnictide families. Allan et al. (p. 563) used scanning tunneling spectroscopy to study the compound LiFeAs. The gap was mapped on three of the five bands on which the Fermi surface resides and was found to be anisotropic in momentum space.

  4. Not So Fast

    Recent observations of some of Greenland's outlet glaciers have shown large and rapid increases in the speeds at which their ice has streamed to the sea. Simple projections of ice loss and sea level rise, based only on these increases, result in alarmingly high values and correspondingly great public concern. In order to provide a more comprehensive and detailed picture of this type of ice sheet mass loss, Moon et al. (p. 576; see the cover) compiled a decade-long record of ice stream velocity measurements for nearly all of Greenland's major outlet glaciers. The pattern of flow variability around the ice sheet was both spatially and temporally complex, with clear differences between marine- and land-terminating types, as well as between regions. Furthermore, the integrated velocity of all of the outlet glaciers measured was considerably less than the upper bounds that have been proposed on the basis of a few rapidly accelerating locations, implying that sea level rise over the next century may be less than the 2 meters that have been suggested.

  5. Magnetic Reconnection

    Magnetic reconnection (MR) has been observed in the magnetospheres of planets with an intrinsic magnetic field, such as Earth, Mercury, Jupiter, and Saturn. MR is a universal plasma process that occurs in regions of strong magnetic shear and converts magnetic energy into kinetic energy. On Earth, MR is responsible for magnetic storms and auroral events. Using data from the European Space Agency Venus Express spacecraft, Zhang et al. (p. 567, published online 5 April; see the Perspective by Slavin) present surprising evidence for MR in the magnetosphere of Venus, which is a nonmagnetized body.

  6. Going to Ground


    Frustrated systems, in which the geometry of the crystal lattice stands in the way of achieving an energetic minimum on all lattice sites simultaneously, have the potential to remain disordered down to the lowest temperatures. Numerous experimental efforts to find a material with a truly fluctuating ground state have failed because ordering often sets in at a finite temperature owing to symmetry breaking. Nakatsuji et al. (p. 559; see the Perspective by Balents) identify the compound Ba3CuSb2O9 as a promising candidate for this state; the Cu-Sb dipoles reside on a hexagonal structure, forming fluctuating spin singlets. Multiple lines of evidence suggest that the material does not order down to the millikelvin temperature range, remaining magnetically isotropic.

  7. Martian Veins

    After more than 7 years of traveling across the Meridiani Planum region of Mars, the Mars Exploration rover Opportunity reached the Endeavour Crater, a 22-km-impact crater made of materials older than those previously investigated by the rover. Squyres et al. (p. 570) present a comprehensive analysis of the rim of this crater. Localized zinc enrichments that provide evidence for hydrothermal alteration and gypsum-rich veins that were precipitated from liquid water at a relatively low temperature provide a compelling case for aqueous alteration processes in this area at ancient times.

  8. Small But Perfectly Formed

    The imaginal discs of Drosophila represent defined larval tissues that give rise to the subsequent adult appendages. These tissues regenerate in response to damage. When the imaginal discs are injured or show tumor growth, they signal to the rest of the larval animal to slow down growth and delay morphogenesis. Garelli et al. (p. 579) and Colombani et al. (p. 582) now show that an insulin-like peptide, termed Dilp8, is secreted into the hemolymph (insect “blood”) and participates in the communication between growing organs and the endocrine system to adjust the growth program and maturation time. This collaboration ensures that adults attain the normal size and maintain appropriate proportions and symmetry.

  9. Not Broken Until Repaired


    Humans, and indeed most eukaryotes, have linear chromosomes with two DNA ends, known as telomeres. Cells have evolved sophisticated systems to repair broken chromosomes, which specifically recognize DNA ends as damage. Telomeres are protected from these repair systems, which would otherwise wreak havoc in the cell, causing genome aberrations that, ironically, can lead to cancer. To understand all the possible threats to telomeres Sfeir and de Lange (p. 593) mutated components of the mouse shelterin protein complex, which forms a protective cap over the telomere ends, rendering telomeres completely devoid of the complex (and packaged only in nucleosomal chromatin). These “naked” telomeres were vulnerable to six DNA repair–related pathways: classical and alternative nonhomologous end joining; ATM and ATR signaling pathways; homology directed recombination; and unmitigated DNA resection.

  10. Blood Pressure Gauge

    Endothelial cells line blood vessels and, by interacting with smooth muscle, can help to control blood flow. Sonkusare et al. (p. 597; see the Perspective by Lederer et al.) describe how signaling in endothelial cells controls contraction of surrounding smooth muscle cells, which provides an important mechanism for control of blood pressure. A calcium-sensitive fluorescent protein was expressed in endothelial cells of mouse arteries to image small changes in calcium concentration that appear to represent opening of single TRPV4 ion channels and consequent influx of calcium into the cell. Clustering of the channels allowed cooperative activation of a handful of channels, which appeared to produce a sufficient calcium signal to open another set of calcium-sensitive potassium channels. The resulting depolarization of the endothelial cells then passes an electrical connection to smooth muscle cells through gap junctions.

  11. Gene Expression by Remote Control

    Techniques that allow remote, noninvasive activation of specific genes in specific tissues could one day be applied to regulate expression of therapeutic proteins in a clinical setting. In a proof-of-concept study, Stanley et al. (p. 604) showed that heating of iron oxide nanoparticles by radiowaves can remotely activate insulin gene expression in cultured cells and in a mouse model. Heating of membrane-targeted nanoparticles induced opening of a temperature-sensitive membrane channel in the cells and triggered calcium entry. The intracellular calcium signal in turn stimulated expression of an engineered insulin gene, leading to the synthesis and release of insulin. In experiments with mice bearing tumors that expressed the engineered insulin gene, exposure to radiowaves promoted secretion of insulin from the tumors and lowered blood glucose levels in the animals.

  12. No Regrets

    As people grow older, the possibility to think about “missed chances” increases. When we are young, thinking about missed opportunities may help to optimize future behavior. However, the older we get the probability of “second chances” decreases and thus the benefit of ruminating upon them disappears. Brassen et al. (p. 612, published online 19 April) studied the behavioral and neural response to missed chances in young adults, the healthy elderly subjects and late-life depressed volunteers. Compared with young and depressed subjects, the healthy elderly subjects showed a reduced sensitivity to missed opportunities. The findings suggest a potential mechanism for preserved emotional health in older age.

  13. Give It Time

    Experimental ecological studies in recent years have provided a great deal of insight into how species diversify and influence ecosystem properties, but in most cases the experiments have been relatively brief (up to ∼5 years). Reich et al. (p. 589; see the Perspective by Cardinale) performed two 13- and 15-year grassland experiments and found that the effects of plant species richness on community-level processes like biomass production tend to be saturating at early stages but that those impacts grow stronger and more linear as experiments run longer. Stronger influences through time were largely driven by increasing amounts of “complementarity” among species, and these trends were correlated with greater expression of functional diversity in multispecies assemblages. Thus, the effects of diversity grow stronger through time as species gain more and more opportunity to vary in their use of the limiting biological resources in their environment, which emphasizes the functional importance of maintaining diversity in ecosystems.

  14. Metabolic Networking

    Understanding complex biological networks, such as those underlying cellular metabolism, requires evaluation not only of the network connections but also the flux through the various biochemical pathways. Schuetz et al. (p. 601) explored the evolutionary constraints that appear to be most critical for the metabolic network in the bacteria Escherichia coli using a combination of experimental tests of reaction flux under various conditions along with mathematical modeling. As a pathway evolves, there are likely to be competing objectives that must be satisfied. Key objectives for the bacterium were strong performance under a given environmental condition, balanced by a requirement for adaptability—minimizing the adjustments required to respond to changed conditions.

  15. Blooming Succession

    Algal blooms in the ocean will trigger a succession of microbial predators and scavengers. Teeling et al. (p. 608) used a combination of microscopy, metagenomics, and metaproteomics to analyze samples from a North Sea diatom bloom over time. Distinct steps of polysaccharide degradation and carbohydrate uptake could be assigned to clades of Flavobacteria and Gammaproteobacteria, which differ profoundly in their transporter profiles and their uptake systems for phosphorus. The phytoplankton/bacterioplankton coupling in coastal marine systems is of crucial importance for global carbon cycling. Bacterioplankton clade succession following phytoplankton blooms may be predictable enough that it can be included in models of global carbon cycling.