This Week in Science

Science  10 Oct 2008:
Vol. 322, Issue 5899, pp. 161
  1. Armor Planting


    Sticklebacks residing in marine settings differ from their freshwater cousins by possessing more protective lateral plates. How does the colonization of fresh water from marine habitats result in this loss of armor plating along the body? Barrett et al. (p. 255, published online 28 August; see the Perspective by Cresko) replicated sticklebacks' natural colonizations from marine to freshwater environments and measured the frequency of alleles affecting plate number among the progeny. Selection against lateral plate development was observed in freshwater habitats but the selection gradient changed over time, with larger (older) fish being more likely to possess reduced armor.

  2. About Africa


    Tropical Africa is an important locus of the global hydrological cycle, and home to a large number of people, but records of how rainfall and temperature have varied in the past are too few and too short to provide a good understanding of what has controlled them over the geologically recent past. Tierney et al. (p. 252, published online 11 September) constructed records of temperature and precipitation from sediments from Lake Tanganyika for the past 60,000 years in order to help to clarify what factors drive climate in the region. Clear links were observed to the Northern Hemisphere and the Indian Ocean, and, surprisingly, changes in the position of the Intertropical Convergence Zone were not the dominant control on rainfall variations. Southeast African climate is thus driven by a complicated, incompletely understood, array of forces.

  3. Triple Cooling

    In contrast to the cold atom regimes of matter vigorously studied over the past decade, a sample of polar molecules cooled to a near stand-still would offer a complex added range of intermolecular interactions. A stumbling block in generating such a sample, however, has been the need to dissipate internal energy tied up in molecular vibrations and rotations. Ni et al. (p. 231, published online 18 September; see the Perspective by Gould) surmount this challenge by using a coherent Raman process, induced by irradiation at two different laser frequencies. The technique yields a translationally ultracold sample of KRb heterodiatomics in the bottom vibrational and rotational levels of the lowest-energy triplet electronic state.

  4. Fluorescing in Sequence

    The capacity of DNA to resist photodamage by rapidly dissipating the energy from ultraviolet light absorption is a key feature of long-term genetic stability. Many model studies have probed the underlying dynamics responsible for this dissipation, but Schwalb and Temps (p. 243) now find that structural simplifications in such studies can be risky. Comparisons of picosecond fluorescent lifetimes for a range of oligonucleotides, both single- and double-stranded, revealed a complex dependence on base sequence. Substitution of four guanine-cytosine pairs into a 20-membered adenine-thymine strand halved the fluorescent lifetime, highlighting a general trend in which mixed sequences relax more rapidly.

  5. Sticky Stuff

    For sticking an object to a wall, an ideal adhesive would have a strong shear adhesive force to counteract gravity, and much lower normal adhesive force to allow for easy removal and reattachment. Significant efforts have been made to mimic the foot of the gecko, because the animal is able to climb almost any surface. Qu et al. (p. 238) demonstrate that vertically aligned carbon nanotube arrays can achieve very high dry shear strength on a variety of surfaces. A thin disordered nanotube layer on top of the aligned nanotube array leads to a significant adhesion anisotropy with shear strengths far exceeding the normal. The shear adhesive force achieved is greater than that of the gecko, creating a strong adhesive affect that can still be moved from one surface to another.

  6. Monitoring Mammalian Conservation Status

    The development of appropriate conservation strategies for global mammalian diversity requires knowledge of effective strategies and details of the current status of at-risk species. Schipper et al. (p. 225) present the key findings of the Global Mammal Assessment, a project involving more than 1700 collaborators in 130 countries and entailing the compilation of standardized data on the distribution and conservation status of all 5487 mammal species (including marine species). The database, made freely available by the International Union for the Conservation of Nature, allows a thorough description of patterns of diversity, threat, and knowledge for all species. Even though apparently quite different patterns were found for marine and land species, the results suggest that they may be underpinned by similar mechanisms. The results also reveal the bleak conservation status of the world's mammals, with one in four land species and one in three marine species under threat. Land species are mainly threatened by habitat loss and by harvesting, while marine species are mainly accidental victims of fishing practices and pollution.

  7. Seising Up Soufrière

    The dynamics of volcanic eruptions coupled with observations of deformation of the ground surface and seismic and geochemical data can provide a view of the plumbing system feeding the volcano. Elsworth et al. (p. 246) integrate such data for the eruption of the Soufrière Hills volcano, Montserrat, which has been ongoing for more than 12 years. Three major eruption cycles have occurred. Correlation of ground inflation and deflation with eruption style and intensity show that magma from the mantle or base of the crust is filling a mid-crustal reservoir continuously, which fills a compliant sub-volcanic reservoir. The data also suggest that the eruption is now nearing its end.

  8. Hot, Deep, and Alone


    Organisms can thrive many kilometers below the Earth's surface in the absence of sunlight and oxygen. Chivian et al. (p. 275) describe the assembly and annotation of a genome from a bacterium in a deep aquifer in a South African gold mine. The genomic analyses and annotation suggest it has the capacity to be a motile, sporulating, sulfate reducing, chemoautotrophic thermophile with a near clonal population structure. This single-species community has a life-style sustained by the hydrolysis of water, which generates hydrogen, as the reductant for energy, and hydrogen peroxide, which oxidizes iron sulfide minerals to sulfate.

  9. A Century in Yosemite

    In the early-20th century, Joseph Grinnell, a founder of ecology, and his colleagues surveyed small-mammal diversity across an elevational transect of 60 to 3300 meters in what is now the Yosemite National Park in California, USA. Their surveys were highly detailed and well-documented, and the data, backed by specimens, field notes, and photographs, have been retained in the Museum of Vertebrate Zoology. Nearly 100 years later, Moritz et al. (p. 261; see the Perspective by Svenning and Condit) resurveyed small-mammal diversity across the Yosemite transect. The results reveal a clear community-scale response to climate warming, with low-elevation species expanding upward and high-elevation species contracting. This century-scale record provides hard evidence for substantial changes in response to past climate change, including the range collapse of some high elevation species. Species diversity has, however, been retained, despite range fluctuations, which suggests the importance of protected landscapes for retaining diversity through migratory responses to climate change.

  10. Promoting Toxin Processing

    Bacterial toxins are often produced as inactive precursors that are activated when they enter eukaryotic cells. One family of such toxins, the Multifunctional Autoprocessing Toxins (MARTX), which includes Vibrio cholerae RTX, are activated by their own cysteine protease domain (CPD) and, recently, the small molecule inositol hexaphosphate (InsP6) has been shown to stimulate this autoproteolysis. Lupardus et al. (p. 265) have determined the crystal structure of the Vibrio cholerae RTX CPD bound to InsP6. Combining the structural data with biochemical and kinetic analysis of CPD mutants suggests that InsP6 binding induces an allosteric switch that exposes the CPD active site and leads to autoprocessing.

  11. T Regulation of Dendritic Cells

    Regulatory T cells act as dampeners in the immune system to prevent overproduction of reactive immune cells and risk of autoimmune disease. T regulatory cells usually inhibit expression of two cell-surface proteins on dendritic cells, CD80 and CD86, which present foreign antigens to the immune system. Wing et al. (p. 271; see the Perspective by Shevach) report that, in mice, CTLA-4, a protein normally necessary for the T regulatory cells to suppress overactivation of dendritic cells, was required to suppress expression of CD80 and CD86. When levels of CTLA-4 were reduced, CD80 and CD86 expression was increased and the dendritic antigen-presenting cells overstimulated other immune cells, resulting in lymphoproliferation, autoimmune disease, and hyperproduction of IgE. At the same time, these mice develop immunity toward tumors. Thus, CTLA-4 in regulatory T cells is responsible for their suppression of dendritic cells and consequently their role in immune system homeostasis.

  12. Mechanics of Atom Clouds

    Cavity optomechanics looks at the effect a few photons trapped within a cavity has on the mechanical properties of that cavity. Such studies can be used in many applications that require tiny movements to be determined (for example, the search for gravity waves), and also in fundamental studies probing the transition from classical to quantum mechanics. Brennecke et al. (p. 235, published online 11 September) introduce a Bose-Einstein condensate (BEC) in which all the atoms are condensed into the same quantum state into an optical cavity and show that the interaction between the BEC and a few photons can be used as an extremely sensitive probe of mechanical oscillation in the quantum regime.

  13. Seismic Signal

    A variety of characteristic earthquakes are recorded before and during volcanic eruptions. Some reflect the movement of magma; others are thought to reflect the fracturing of rock and movement or decompression of heated water near the magma. Benson et al. (p. 249; see the Perspective by Burlini and Di Toro) are able to produce many of these in a laboratory sample at conditions relevant to volcanic reservoirs. The authors recorded microquakes around a fractured sample as pore water was rapidly decompressed. The location and type of quakes in the sample are similar to those recorded at many active volcanoes, including a characteristic low-frequency signal that might be useful for eruption forecasting.

  14. Shifting the Range

    The literature on biotic range shifts under anthropogenic climate warming focuses mainly on temperate climates, where lowland species can escape warming either by poleward latitudinal shifts or by upslope elevational shifts. Because the latitudinal temperature gradient is almost zero between the Tropics of Cancer and Capricorn, the most likely escape for lowland tropical endemics is upslope rather than poleward. There are no lower-latitude pools of species already adapted to even warmer climates, waiting to fill a lowland void. Using biogeographical range data for nearly 2000 species of plants and insects along a tropical elevational gradient in Costa Rica, Colwell et al. (p. 258; see the Perspective by Svenning and Condit) reveal potential patterns of substantially decreased lowland species richness and early gaps between current and postwarming elevational ranges. Assuming a 600-meter upslope shift driven by a 3.2°C temperature increase over the next century, half of these species may no longer occupy the lowlands and half may be faced with gaps between their current ranges and postwarming ranges.

  15. Hindering Herpes

    Reactivation of herpes simplex virus (HSV) from neuronal latency is a common and potentially devastating cause of disease worldwide. Now Knickelbein et al. (p. 268) demonstrate the use of the lytic granule components perforin and granzyme B by HSV-specific CD8+ T cells in maintaining HSV-1 latency in sensory neurons both in vivo and in vitro. Lytic granules polarized to T cell/neuron junctions during immunosurveillance of latently infected neurons, which are selectively resistant to apoptosis induction by HSV-specific CD8+ T cells. The lytic granule component, granzyme B, inhibited viral gene expression through cleavage of a viral immediate early protein required for expression of early and late genes. Thus lytic granules can function in a noncytotoxic manner and granzyme B targets a viral protein that is required for further viral gene expression.

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