Editors' Choice

Science  15 Oct 2004:
Vol. 306, Issue 5695, pp. 375
  1. Ecology/Evolution

    In the Short Grass

    The unpredictability of the movements of groups and populations of grazing animals causes difficulties for the conservation and management of their rangelands. The shifting mosaic of forage production, grazer occupation, and predator distribution depends on a web of climatic, physiological, and behavioral variables — factors that tend to be measured and modeled at different spatial and temporal scales. By linking behavioral models and 2-year spatial censuses over 1600 km2 of the Serengeti plains, Fryxell et al. attempt to predict the spatial distribution of Thomson's gazelles in East African grasslands. They first compared the power of several different foraging models examining the contribution to the animals' relative fitness of hourly or daily food (energy) intake. Daily energy intake was the best predictor of gazelle's occupation of short-grass patches. They then compared seven further models of animal movements and found that gazelles move to neighboring patches with a probability that is proportionate to the potential energy gain. These results help explain why populations of grazers can require such large areas, and they will help in the formulation of management strategies to ensure long-term success. — AMS

    Ecology 85, 2429 (2004).

  2. Materials Science

    Making Flame Retardant

    Polymeric flame-retardant materials are typically made by blending traditional polymers with flame-retardant phosphorous or halogenated compounds. The most commonly used brominated additives have drawbacks due to the release of toxic and corrosive halogenated gases during combustion and because they impart a strong color to the polymer. The compounds also appear to be environmentally persistent. Siloxane-based mixed organic-inorganic polymers, such as polycarbosiloxanes, also have good flame- retardant properties but are difficult to synthesize with high molecular weight because of the physical and chemical differences of the constituent components. Using both crude and immobilized lipases—enzymes that hydrolyze lipids—Kumar et al. were able to catalyze the transesterification reaction to connect various diesters and diamides to siloxanes. Of the lipases that were tested, Novozyme-435 had high efficiency in catalyzing the reaction without inducing undesired cross reactions. The polymers were synthesized without solvent under vacuum conditions and were of much higher molecular weight and lower polydispersity than those obtained using solvent or vacuum chemical methods. The best materials showed heat resistance up to 400°C. All the materials tested had little residual char after heating to 1200°C, indicating almost complete decomposition, and produced no toxic materials. — MSL

    Adv. Mat. 16, 1515 (2004).

  3. Plant Biology

    Creeping Pollen

    One of the potential risks associated with introducing new genomes into crop plants is the spread of undesirable genes to other plants. Any genome, whether derived through the use of transgene technology or through more traditional genetic means, may be a source of genes spreading through related populations. Creeping bentgrass, Agrostis solonifera, is a wind-pollinated grass that is widely used on golf courses and as a forage crop. The first flowering of a modified version of creeping bentgrass into Oregon fields in 2003 offered an opportunity to follow the initial gene flow from this crop. The creeping bentgrass was genetically modified to express a gene conferring resistance to the herbicide glyphosate. Watrud et al. distributed nontransgenic A. solonifera and other compatible plants in the regions where prevailing wind conditions would suggest that pollen might travel. Analysis of offspring from these “sentinel” plants indicated that most of the pollen-mediated gene flow occurred in the direction of prevailing winds within 2 km of the source plants. The greatest distance of observed gene flow was 21 km. — PJH

    Proc. Natl. Acad. Sci. USA 101, 14533 (2004).

  4. Medicine

    TB in the Hot Zone

    A worrying characteristic of tuberculosis (TB) nowadays is its ability to generate “hot zones” of multi-drug-resistant strains of Mycobacterium tuberculosis. Blower and Chou have developed an amplifier model by which they can track the emergence and evolution of strains into hot zones that have serially accumulated resistance to several drugs, and they have verified their model with World Health Organization data. Paradoxically, it seems that high-intensity control measures, which have most successfully reduced the incidence of sensitive strains, may have promoted the emergence of hot zones, even when the resistant strains are less fit and less transmissible. This is because if strains of bacteria escape cure, the victims of such resistant TB stay infectious for longer and the bacteria may thus go on to accumulate more modes of resistance. Nevertheless, there is time to act: The model also indicates that even after 30 years of poor drug control, only low levels of multi-drug resistance emerge. Regionally customized control programs could thus be developed to deal with local varieties and combinations of drug-resistant strains. — CA

    Nature Med. 10, 1111 (2004).

  5. Physics

    Counting Atoms

    Success in the emerging field of quantum information science will be dependent on the ability to impart and carry information reliably in single quantum units such as atoms, ions, or photons. Cavity quantum electrodynamics is one proposal in which a single atom trapped in a cavity interacts with a single photon also trapped within the cavity. However, loading the cavity with atoms is somewhat statistical in terms of the number of atoms loaded in one cycle. McKeever et al. have developed a diagnostic technique allowing them to monitor the number of atoms present within the cavity. The atoms fluoresce in response to a near-resonant probe beam, and as the atoms leave the cavity one by one, a corresponding stepwise change in the transmission can be observed. Knowing exactly how many atoms are within the cavity at any given time should provide the basis for precise atom-atom and atom-photon interactions crucial for the implementation of quantum information protocols.— ISO

    Phys. Rev. Lett. 93, 143601 (2004).

  6. Chemistry

    Untangling Oxidation

    Small gold clusters adsorbed on transition metal oxides, such as TiO2, exhibit unusually high activity as oxidation catalysts. One possible explanation for this enhanced reactivity compared to bulk gold surfaces is that these small clusters more readily dissociate molecular O2, but theoretical calculations and photoemission studies on gas-phase gold clusters suggest that O2 dissociation is a highly activated process. Stiehl et al. studied the oxidation of CO to CO2 over gold clusters that ranged in size from 2 to 5 nm adsorbed on a TiO2(110) surface. A molecular beam source and collision-induced desorption were used to create surfaces covered only with dissociated oxygen and surfaces covered with a mixture of atomic and molecular oxygen. CO2 production increased by about 40% for a surface with both types of oxygen species, as opposed to one with only atomic oxygen. Thus, there are oxidative reaction channels over supported gold clusters that do not require the direct participation of dissociated oxygen. — PDS

    J. Am. Chem. Soc. 10.1021/ja046390x (2004).

  7. Biomedicine

    Weight Displacement Activity

    As all dieters know, the key to weight loss is altering the balance between energy intake and energy expenditure. At the molecular level, one of the major regulators of energy balance is PGC-1α, a nuclear protein that stimulates the transcription of genes involved in diverse metabolic processes such as glucose production in the liver and mitochondrial function in fat and muscle.

    A new study of PGC-1α-deficient mice by Lin et al. confirms the protein's central role in metabolic control but also reveals some surprises. Rather than being prone to weight gain, as predicted by earlier cell culture studies, the mutant mice stayed lean, even when on a high-fat diet. This effect was due, at least in part, to increased energy expenditure: Mice lacking PGC-1α were profoundly hyperactive, showing a 40% increase in random movements as compared to control mice. The mutant mice also showed behavioral disturbances and had brain lesions reminiscent of those seen in certain neurodegenerative disorders, such as Huntington's disease. Interestingly, these brain disorders have been linked previously to defects in mitochondria, whose function is known to be regulated by PGC-1α in other tissue types. — PAK

    Cell 119, 121 (2004).