Editors' Choice

Science  07 Mar 2008:
Vol. 319, Issue 5868, pp. 1309

    A Flashy Affair

    1. Caroline Ash

    Humans see chameleons as masters of camouflage. The lizards themselves seem to see more in it than predator avoidance. This family of lizards has evolved a range of talents, some merely changing skin tone, others changing color, too. All thanks to rapidly reacting neurally controlled chromatophores in their skin. Stuart-Fox and Moussalli used reflectance spectroradiometry, tuned to the spectral sensitivities of the retinas of chameleons and of potential bird predators, to measure the conspicuousness of a variety of lineages of African dwarf chameleons in their preferred habitats. If the habitat is dense and complex, bird predators tend to be excluded, and there is less need for disguise. Here, the chameleons indulge in flashy aggressive behavior, changing color spectacularly in social displays; at least from a chameleon's-eye view. In more open, hotter habitats it pays to live a drab and quiet life, avoiding the notice of predators, staying cool sand-colored and merely adjusting brightness during social exchanges. So, deep in the bush, what we perceive as subtly changing camouflage, chameleons perceive as flamboyant social signaling. — CA

    PLoS Biol. 6, e25, 10.1371/journal.pbio.0060025 (2008).


    All Stirred Up

    1. H. Jesse Smith

    Around 55 million years ago, at the height of the Paleocene-Eocene thermal maximum, the world was a much warmer place than today. Sea surface temperatures were higher everywhere than now, and the equator-to-pole thermal gradient was much shallower. Climate for much of the past 500 million years has been warmer than it is now, and during the warm periods the surface meridional temperature gradient generally appears to have been weak. Explaining how the climate system might have transferred heat from low to high latitudes to maintain such a shallow thermal gradient has been difficult, and many hypotheses have been advanced, including those involving effects from radiative forcing by high concentrations of atmospheric carbon dioxide, more intense ocean heat transport, differences in the amounts and locations of polar stratospheric clouds, and extratropical atmospheric convection. Korty et al., using a coupled model of intermediate complexity, investigate another possibility: that tropical cyclones could have caused enough ocean surface mixing in the tropics to cool the sea surface there and drive the strong poleward heat flux needed to produce the shallow thermal gradients that seem to have prevailed during warm climates. This solution, if correct, also has implications for how we might expect the climate system to respond to anthropogenic warming. — HJS

    J. Clim. 21, 638 (2008).


    Anyone for a Cuppa?

    1. Gilbert Chin

    Inhaling the soothing aroma from a mug of peppermint tea renews the sense of wonder at the delightful mix of monoterpenes produced by the hybrid plant Mentha X piperita. Its oil, which accumulates within a structure called a peltate glandular trichome, contains high levels of (-)-menthol and low levels of the precursor (+)-pulegone and the side product (+)-menthofuran. The critical balance between the activities of pulegone reductase (which produces menthones that are converted into menthols) and menthofuran synthase (which diverts pulegone into menthofuran) can be disturbed in less-than-ideal environments, such as low light.

    Rios-Estepa et al. have collected the measured biochemical parameters of kinetic constants and metabolite concentrations, validated them where feasible against independently derived quantities (gland volume, oil density, and terpene molecular weight), and built a biosynthetic model that simulates the developmental time courses under optimal and low-light conditions of menthol, pulegone, and menthofuran levels. An earlier genetic engineering study had suggested that menthofuran turned down the transcription of pulegone reductase, but plugging this constraint into the model failed to reproduce the observed changes in terpene levels. Instead, the observations could be replicated by assuming that menthofuran acted as a competitive inhibitor of the reductase, a supposition confirmed by Lineweaver-Burk analysis of in vitro enzyme assays. — GJC

    Proc. Nat. Acad. Sci. U.S.A. 105, 2818 (2008).


    A Fruitful Fuel Proposal

    1. Phil Szuromi

    Sustainable alternatives to gasoline and diesel fuels will need to recapitulate some of the properties that make currently used fuels attractive energy carriers, such as low vapor pressure and stable long-term storage. Horváth et al. examined the properties of one such alternative, γ-valerolactone (GVL)—a small cyclic ester produced by fruits and used as a food additive. Compared to methanol, ethanol, and methyl and ethyl tert-butyl ethers, GVL has a much lower vapor pressure, which reduces volatile emissions, and also low melting and flash points that facilitate safe storage. It is not readily hydrolyzed to the acid under pH-neutral conditions, nor does it readily form peroxides. Because GVL does not form an azeotrope with water, less energy is needed to recover it through distillation. The authors have explored catalytic routes to GVL from sucrose and conclude that with further advances in synthetic efficiency from biomass, GVL could serve as an oxygenated fuel additive or even a fossil-fuel replacement on its own. — PDS

    Green Chem. 10, 238 (2008).


    Vapors Plucked on a Harp

    1. Ian S. Osborne

    Optical or electronic devices that sniff out chemical compounds with high sensitivity and selectivity clearly have applications in a broad range of circumstances, from environmental monitoring to the detection of biohazards. However, the compounds of interest may not be in pure form; often they are diluted among multiple background substances, and such an artificial nose must therefore be able to sort through complex mixtures. Stievater et al. present a chemical sensor based on a micro-optomechanical bridge that can be interrogated remotely using optics. Their device, a microharp, forms one end of a Fabry-Perot interferometer and comprises an array of microbridges in which each bridge is coated with a sorbent polymer sensitive to a particular analyte. Each bridge also has a distinct length and so vibrates at an individual frequency. When the device is placed in a test atmosphere, different compounds bind to particular strings on the harp, changing the mass of the bridge and thereby inducing a shift in the frequency at which it vibrates. Interrogating the vibrational frequency of each bridge separately allows monitoring of a vapor's chemical composition remotely, and in some cases (as for organophosphonates) detection concentrations down to 17 parts per billion. — ISO

    Opt. Express 16, 2423 (2008).


    Doing Double Duty

    1. Stella M. Hurtley

    During cell division, centrosomes are important in the organization and maintenance of the mitotic spindle. Fielding et al. found that a kinase, integrin-linked kinase (ILK), known to be important in cell adhesion, also interacts with centrosomal and spindle proteins, including the main constituent of the mitotic spindle, tubulin. When ILK was inhibited, cells failed to assemble mitotic spindles properly, resulting in aberrant chromosome segregation. The centrosomal protein RUVBL1 was important for ILK targeting to the centrosome, and the activity of ILK was important for another centrosomal protein, ch-TOG, to promote spindle pole organization and mitosis. This unanticipated role for ILK in promoting centrosomal organization, spindle assembly, and chromosome segregation may represent an important link between cell adhesion and mitosis. — SMH

    J. Cell Biol. 180, 681 (2008).


    An Autism Association

    1. Barbara R. Jasny

    Although autism is highly heritable, sorting out the genes associated with this complex disease has been difficult. Weiss et al. searched for structural mutations (duplications or deletions below the level of microscopic detection) in the genomic DNA of 751 families who are part of the Autism Genetic Resource Exchange. They found a significant association of autism with a nearly 600-kb region that was deleted or duplicated at a locus on chromosome 16. This structural mutation was also observed in patients from Children's Hospital in Boston and in a group from Iceland. It occurred at a frequency of approximately 1% in patients as compared with less than 0.1% of the general population. It might result from unequal crossing over at this region of chromosome 16, which is a known hotspot for deletion and duplication and is bordered by two duplicated regions. Autism may represent the summation of a series of rare events, whose detection will require screening tens of thousands of patient samples. — BJ

    N. Engl. J. Med. 358, 667 (2008).