This Week in Science

Science  24 Jun 2005:
Vol. 308, Issue 5730, pp. 1837
  1. A Changing Climate for Fish and Chips


    Climate change is well established as a potential threat to biodiversity and the services and benefits that people gain from ecosystems. Perry et al. (p. 1912, published online 12 May 2005) examined the effects of climate change on a key ecosystem service, marine fisheries. Many species have exhibited a strong northward shift during the last 25 years in the North Sea. Many commercially important fish such as cod, whiting, and anglerfish have shifted from 50 to 800 kilometers northward. If current climate trends continue, some species may have withdrawn completely from the North Sea by 2050.

  2. Paleocene Warming at Depth

    The Paleocene-Eocene Thermal Maximum (PETM) was a geologically brief period of warming that occurred about 55 million years ago. During this episode, the global carbon cycle was significantly perturbed, as reflected by a large and sudden change in the carbon isotopic composition of the global active carbon pool. This perturbation may have been caused by a massive release of methane hydrates from the sea floor, but the cause of such a release is not understood. Tripati and Elderfield (p. 1894) present benthic ocean temperature records from intermediate-depth waters in both hemispheres and near the equator which show that all of those locations warmed roughly equally, by 4° to 5°C, slightly ahead of the corresponding changes in the carbon system. These data are consistent with the idea that destabilization of methane clathrates in marine sediments were involved as a source of the isotopically anomalous carbon during the event.

  3. Thicker in the Middle

    The mass balance of Antarctica's ice sheets is a critical parameter in any evaluation of the potential sea level rise that would accompany global warming. Davis et al. (p. 1898, published online 19 May 2005; see the Perspective by Vaughan) report results, derived from measurements made by satellite radar altimetry conducted from 1992 to 2003, which show that large parts of the interior of Antarctica gained mass during that time. They attribute this increase to a rise in precipitation in East Antarctica, an effect that has been suggested to accompany global warming. The mass balance of the entire ice sheet is still uncertain, however, because mass loss in areas near the coast that are not accessible to this technique could be even greater than the gains seen in the interior.

  4. Assessing a Hydrogen Future


    The pollution reductions and health gains that would follow from powering cars and trucks with hydrogen are well understood in principle, but a detailed analysis of those benefits would be useful. Jacobson et al. (p. 1901) present such a model study of the effects of converting the entire United States vehicle fleet to hydrogen fuel cells or fossil fuel-electric hybrid vehicles. The use of hydrogen fuel cell vehicles reduces pollution and adverse health effects in all cases, but to what extent depends on how the hydrogen is produced. In the best case, the generation of hydrogen by wind power may make it a more economical fuel than gasoline when all costs are considered.

  5. Weighing Earth's Core

    Seismic velocities and comparisons with experiments have been used to infer the density of Earth's interior, often through a linear extrapolation known as Birch's Law. This analysis has indicated that Earth's inner core is mostly an iron-nickel alloy that must contain some light elements, such as sulfur or oxygen. However, this inference requires knowledge of how seismic velocities vary, not just with density but also temperature. Lin et al. (p. 1892) directly measured seismic velocities in iron at high pressure and at several temperatures. Temperatures comparable to those in the deep Earth reduce the sound velocity relative to the inferred density. Thus, Earth's core requires more light elements than indicated from a linear relation with density, a finding more consistent with other inferences.

  6. Burning Up

    Understanding fire is one of the oldest challenges in chemistry. Spectroscopy studies of flames can identify molecular fragments, which then serve as input for kinetic models that sort out the many steps whereby hydrocarbons are oxidized into water and CO2. In these models, carbonyl compounds are well-established intermediates, but their less stable enol tautomers, which bear an OH group bound to a C=C double bond, are not. Taatjes et al. (p. 1887, published online 12 May 2005; see the cover) have now observed significant amounts of two-, three-, and four-carbon enols in flames burning commercial gasoline constituents. A clean, low-temperature hydrocarbon oxidation is achieved by tyrosinase enzymes, in which two copper ions in the active site bind O2 and catalyze the formal insertion of an O atom into an aromatic C-H bond in phenol. Synthetic chemists have assumed that the hydrocarbon interacts with the bound O2 before it cleaves. Mirica et al. (p. 1890; see the Perspective by Reedijk) present evidence from a model complex that suggests a different pathway. Spectroscopic studies of a compound in which a copper dimer mimicks the O2 binding site of the enzyme reveal a reactive intermediate at −120°C in which the O2 bond is broken before oxygen transfer to a phenol derivative. These results suggest that the enzymatic oxidation could likewise involve phenol attack on an electrophilic copper (III) bridging oxo species.

  7. Absent Allies

    A major difficulty in developing a vaccine against human immunodeficiency virus (HIV) is the high level of escape by the virus when it encounters antibodies within each host. Nevertheless, a small handful of monoclonal antibodies broadly specific for HIV can neutralize the virus, and they have been studied carefully with the hope of understanding why similar antibodies are not generated easily during a normal immune response. Haynes et al. (p. 1906, published online 28 April 2005; see the Perspective by Nabel) find that two of the monoclonal antibodies possess a range of specificities and react against the human phospholipid, cardiolipin. Thus, broadly neutralizing antibodies may be seen so rarely in HIV infection because the very features that endow anti-HIV properties also make them self-reactive and, as such, they are not tolerated by the body's immune system.

  8. Catalase for Longer Life


    Cell and tissue damage caused by free radical oxygen molecules have been linked to aging pathologies, yet the idea that antioxidant defenses can prolong life has been controversial. Schriner et al. (p. 1909, published online 5 May 2005; see the Perspective by Miller) generated transgenic mice that overexpress catalase in mitochondria, a major source within the cell of oxygen free radicals. Catalase removes damaging hydrogen peroxide that can generate reactive oxygen species. In the transgenic mice, cellular oxidative damage and age-related decline in heart function were reduced and cataract formation was delayed. In addition, life span increased by nearly 20%. Thus, antioxidant enzymes can promote mammalian longevity.

  9. Calling New Neurons

    Most neurogenesis in the brain occurs in the context of early development. However, even through adulthood, a steady stream of newly generated neurons supplies the olfactory bulb. Neuronal progenitors from the subventricular zone of the brain migrate together as a chain to the olfactory bulb. Ng et al. (p. 1923) have now identified prokineticin 2 (PK2) as one of the signals that calls the neurons to their destination. Prokineticin proteins are secreted, and in other locations also regulate processes such as gastrointestinal motility and pain sensitization. The mammalian retina, like other regions of the brain, develops in a sequential manner. Cells of a given function are born earlier, whereas those born later are dedicated to other functions. Kim et al. (p. 1927) have clarified how one signaling molecule, growth and differentiation factor 11 (GDF11), affects this trajectory of differentiation in the retina differently than in the olfactory epithelium. In the developing retina, GDF11 does not affect proliferation of progenitor cells, as it does in the olfactory epithelium, but signals to the progenitor cells competence to produce certain types of differentiated cells

  10. Alarming the Mob

    Although there has been much interest in the function and evolution of alarm signals in animals, few studies have been able to control the presentation of predators to prey species and elucidate any complexity of meaning that might be encoded in these signals. Templeton et al. (p. 1934; see the news story by Miller) exposed black-capped chickadees, a common North American songbird, to various different species and sizes of predator. Chickadees living in small flocks responded to alarm calls by mobbing the threatening predator. Spectrographic analyses showed striking differences in chickadee alarm calls that correlating strongly with the size and threat of the potential predators. Furthermore, the chickadees responded to recordings of the different alarm calls by varying their mobbing behavior.

  11. Agrin Yes, Neuregulin No

    Neuromuscular junctions develop through a series of reciprocal interactions between the muscle fiber and the incoming motor neuron. Both agrin and neuregulin have been implicated in neuromuscular junction development. Escher et al. (p. 1920) use targeted gene ablations to clarify which molecules act when. It seems that neuregulins are not critical for neuromuscular junction formation, but agrin is. The previously observed effects of neuregulin signaling disruptions on neuromuscular junction formation may well have been mediated indirectly through the effects of neuregulins on Schwann cells, which surround the neuromuscular junction.

  12. OOOH Aaah

    The chemistry of Earth's upper atmosphere is dominated by small open-shell molecules, that form in the abundance of ultraviolet radiation and persist until they react via collisions. Despite years of direct observation and model studies, the properties of many of these fleeting species remain elusive. Suma et al. (p. 1885, published online 5 May 2005) prepared the OOOH radical, a weak adduct of OH and O2, by electric discharge in an oxygen-water vapor mixture, and probed its structure by microwave spectroscopy. Although not yet observed outside the laboratory, OOOH has been proposed in models of atmospheric OH chemistry. The spectra support a Z-shaped trans geometry, in contrast to theoretical predictions of a cis structure.

  13. Community Proteomics

    Large-scale, cultivation-independent analyses of microbial genetic potential will be important in order to understand organisms in the contexts of their natural environments. By combining both genomics and proteomics to study the metabolism of natural biological communities, Ram et al. (p. 1915, published online 5 May 2005) were able to confidently detect 2033 different proteins that derived from five dominant biofilm members without any need to culture the organisms. Overall, about 17% of the genes of these organisms were detected, but for the dominant biofilm member, Leptospirillum group II, as many as 48% of the predicted proteins were revealed.

  14. Making for Sensitive Smelling

    Receptors that couple to a heterotrimeric GTP-binding protein (G protein) are thought to stimulate a large number of G protein molecules. This model of signal amplification is based primarily on quantitative studies of phototransduction in vertebrate retinal cells. Bhandawat et al. (p. 1931) have examined signal transduction by olfactory receptors in frog olfactory neurons. Quantal analysis of receptor responses to odorant ligands suggests that an activated odorant receptor, probably due to an extremely brief dwell time of odorant-receptor interaction, has a low probability of stimulating a single G protein molecule. High sensitivity to odorants might still be achieved with repetitive odorant binding and by signal convergence in the olfactory bulb.