Editors' Choice

Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1842

    Color Convergence in Columbines

    Anthocyanins are pigment molecules commonly found in red, blue, and purple flowers. Columbine flowers are imbued with anthocyanins, and this plant is known to have undergone a recent and rapid divergence, most likely as a result of strong selection by pollinators for floral traits such as color.

    Using a phylogenetic framework, Whittall et al. have investigated the convergent loss—that is, the loss of the same trait across multiple evolutionary lineages—of anthocyanin biosynthesis in columbines, which has resulted in flowers that are yellow or white. They found six independent losses (four fixed and two polymorphic) and no gains of floral anthocyanins. Quantitating the anthocyanin precursors in three species without anthocyanin loss and eight species with loss demonstrated that the loss of anthocyanin correlated with a broad convergence in the reduced expression of genes that occur in the later stages of the biosynthetic pathway. Additionally, two of these genes are regulated by a single gene and demonstrated a correlated reduction of expression in five lineages, suggesting that the mutation causing anthocyanin loss is a regulatory component and not a structural one (enzyme). These data show that there is an evolutionary constraint on some of the genes in anthocyanin biosynthesis, most likely because upstream intermediates are also useful in protecting plants against UV damage, insects, and pathogens. — LMZ

    Mol. Ecol. 15, 4645 (2006).


    Taste and Timing

    Modern water treatment protocols have gone a long way toward the efficient elimination of toxic contaminants in municipal supplies. However, certain benign impurities may remain and give rise to unpleasant tastes or odors. One challenge in adopting a general strategy for treating such “T&O” compounds is their varying proportions in different water sources. Effective remediation thus requires detailed knowledge of the distinct chemistry of each substance.

    Toward this end, Peter and von Gunten present a systematic study of the oxidation kinetics of 11 common organic T&O contaminants by both ozone and hydroxyl radicals. The targets, spanning a variety of alcohols, aldehydes, ketones, and ethers, were treated individually with the oxidants in ultrapure water, and measured rate constants were then used to predict the degradation kinetics observed in spiked samples of natural water from two different lakes. In general, the predictions and measurements showed strong agreement. Five of the compounds were very efficiently oxidized by ozone, with rate constants of ∼105 M−1s−1. Trihaloanisoles proved the most resistant to preliminary ozonation but were rapidly degraded by hydroxyl radicals. The authors note that hydroxyl radical protocols would need to be applied carefully to avoid excessive production of toxic bromate ions from residual aqueous bromide salts. — JSY

    Environ. Sci. Technol. 10.1021/es061687b (2006).


    Mopping Up Little Helpers

    Sponges (Porifera) hold an interesting evolutionary position (sitting between the choanoflagellates and other animals), being conglomerations of cells, with some functional and morphological differentiation, loosely organized around a spongocoel cavity. Many sponges host an array of prokaryotes, some of which may accumulate passively as the sponge filters seawater; indeed, one view is that the sponge cells serve merely as an inert scaffold for prokaryote communities.

    However, Sharp et al. show in a 3-year study that this association can persist beyond happenstance. They find that sponge embryos travel with a contingent of prokaryotes that are inherited vertically, implying that there are selective mechanisms of transmission and recruitment. Like the somatic cells of the sponge, the prokaryotic denizens display a functional differentiation, with some specializing in sulfur oxidation or nitrogen fixation, and they probably contribute to mutualistic nutrient cycling within the sponge. Furthermore, some of the bacteria appear to produce bioactive compounds, which may aid host defenses. — CA

    Appl. Environ. Microbiol. 10.1128/AEM.01493-06 (2006).


    Copper Confinement

    As microelectronic circuitry continues to shrink, and devices are packed onto chips at increasingly higher densities, two main concerns must be addressed: heat dissipation and interconnection reliability. Copper has therefore begun to replace aluminum as the metal of choice for on-chip wiring, on account of both its lower resistivity (which reduces heat generation) and its resistance to electromigration. However, Cu tends to diffuse rapidly into silicon, generating electronic traps within the Si bandgap that are detrimental to device performance. To address this shortcoming, the use of diffusion barriers between Si and Cu is being explored. The materials composing such barriers must be compatible with the fabrication process and also resistant to recrystallization during the high-temperature processing steps, a typical cause of failure. Hafnium nitride (HfNx), with a melting temperature exceeding 3300°C, has attracted strong interest in this vein. Rawal et al. have investigated the combined use of thin layers of Ge/HfNx as a diffusion barrier. They find that the bilayer system is more effective than a single HfNx barrier layer, a result that they attribute to the ready reaction of Ge with Cu to form Cu3Ge, thereby immobilizing much of the Cu that could otherwise diffuse through the HfNx layer. — ISO

    Appl. Phys. Lett. 89, 231914 (2006).


    Glass at a Crash Site

    Hundreds of thousands of years ago, Stone Age peoples inhabited the Dakhleh Oasis, in central western Egypt, when the ancient landscape included lakes. The area has attracted substantial archaeological and geological investigation, and one unresolved mystery has been the origin of unusual darkly colored glass, termed “Dakhleh glass,” found at the site. Osinski et al. have probed the glass using x-ray fluorescence techniques, isotopic analysis, and electron microscopy. Its chemical composition (in particular, an anomalously high proportion of CaO and Al2O3) differs from that of all known volcanic glasses, and there is no evidence of volcanism in the region. The authors argue that the glass was probably created through a meteorite impact occurring 100,000 to 200,000 years ago. The energy of the impact would have fused the local carbonate and sandstone rocks into glass. The imprints of plant stems and leaves from that time were also uncovered in the glass, but no signs of shock metamorphosis were evident. Because an impact crater has not yet been located, the authors note the possibility of an aerial burst; in either case, such an event would have devastated the local population. — JB

    Earth Planet. Sci. Lett. 10.1016/j.epsl.2006.10.039 (2006).


    A Conservation of Clouds

    DNA sequencing and careful morphometric analysis can reveal hidden differences between populations of organisms originally considered members of a single species, which can lead to their reclassification as two or more species. Such taxonomic splitting can have important implications for conservation if, for example, an already rare species turns out to be two or more even rarer ones.

    The clouded leopard, Neofelis nebulosa, is such an example. This increasingly rare animal is found in the tropical forests of Southeast Asia, with the subspecies N. n. nebulosa occurring on the mainland and the subspecies N. n. diardii on the islands of Borneo and Sumatra. Buckley-Beason et al. compared nuclear and mitochondrial DNA sequences from several mainland and island individuals, and they concluded that the genetic differences were at least as great as those among other large cat species (lion, tiger, leopard, jaguar, and snow leopard). Kitchener et al. compared the coat patterns of a larger sample of individuals and found clear evidence for two distinct groups on the basis of the size and shape of the clouds on the shoulders of these animals; they recommend that the clouded leopard now become two distinct species, N. nebulosa and N. diardii. — AMS

    Curr. Biol. 16, 2371; 2377 (2006).


    'Tis the Season

    Although the giving of gifts is a common activity at this time of year, giving a gift certificate has become an allowable substitute for giving money, which is generally regarded as unseemly. In order to explore whether money can serve not only as a useful instrument (for the purchase of material goods) but also as a valued resource, Briers et al. have carried out a series of experiments to see whether an unfulfilled desire for food (or money) might make one more tight-fisted (or more voracious). People who were hungry behaved less generously toward a charity (Médecins Sans Frontières) and in public goods games than those who had just eaten cake; conversely, people who were told to imagine being desirous of a substantial payoff (being in such a state was confirmed by how much their estimates of the size of a coin were skewed to be larger than actual) consumed more M&M's than those who were focused on a modest windfall. These results linking the rewarding character of food to that of money dovetail neatly with a recent study (Vohs et al., Reports, p. 1154, 17 November 2006) that demonstrated money's value as a means of enhancing one's self-sufficiency and social independence. — GJC

    Psychol. Sci. 17, 939 (2006).