This month in Science Roundup


On the Move
http://www.sciencemag.org/cgi/content/summary/313/5788/775

During the evolution of life, the ability to migrate and disperse becomes ever more sophisticated, enabling journeys thousands of kilometers long. Such travels shape the life history of a species and the ecology of the places it visits. A special section of the 11 Aug 2006 *Science* explored some of the advances in our understanding of life on the move. News stories looked at studies of the effects of climate change on marine migrants, technological innovations for tracking animals from jellyfish to polar bears, genetic and environmental influences on bird migration, and the emerging principles of "movement ecology." A series of Perspectives explored various aspects of plant and animal dispersal, the motivation for insect migration, and conflicting evidence about long-distance navigational mechanisms used by animals (particularly birds). A related Report described the role of polarized light at dawn and dusk in calibrating the magnetic compasses of migratory songbirds. And a Review article presented new archaeological and genetic perspectives on the dispersal of modern humans out of Africa some 40,000 to 60,000 years ago.


Irrationality in the Brain

Theories of economic decision-making have traditionally assumed that humans are fundamentally rational. However, simply casting an option in a positive or negative way can have a dramatic influence on the choices we make -- a phenomenon known as the framing effect. For example, given the choice between packages of meat labeled "80% lean" or "20% fat," most people would choose the "80% lean" package even though the meat in each is exactly the same. In a study reported in the 4 Aug 2006 *Science*, De Martino et al. ( http://www.sciencemag.org/cgi/content/short/313/5787/684 ) investigated the neurobiological basis of the framing effect by means of functional magnetic resonance imaging (fMRI) and a novel financial decision-making task. They found that the framing effect was specifically associated with activity in the amygdala, a brain region associated with learning and emotion. Moreover, the researchers were able to predict which individuals were relatively immune to the framing effect, and perhaps the most rational, based on activity in another brain region called the orbital and medial prefrontal cortex. The more activity subjects had in this area, the less susceptible they were to the framing effect. G. Miller highlighted the findings in an accompanying News story ( http://www.sciencemag.org/cgi/content/short/313/5787/600b ), and in a segment of the 4 August *Science* podcast ( http://www.sciencemag.org/about/podcast.dtl#20060804 ).


Vietnam’s Psychological Toll

The prevalence of posttraumatic stress disorder (PTSD) in Vietnam veterans has been a subject of heated debate since 1988, when two major government-funded studies reported widely divergent rates of the disorder. Whereas the Centers for Disease Control reported that 14.7% of Vietnam veterans had developed PTSD and that 2.2% were suffering from it 11 to 12 years after war ended, the National Vietnam Veterans Readjustment Study (NVVRS) reported rates of 30.9% lifetime PTSD and 15.2% current PTSD. Interest in the accuracy of these figures has intensified as comparisons are now being made between the Vietnam War and the ongoing conflict in Iraq. In a Report in the 18 Aug 2006 *Science*, Dohrenwend et al. ( http://www.sciencemag.org/cgi/content/short/313/5789/979 ) presented a rigorous reanalysis of PTSD prevalence among Vietnam veterans using military records, historical accounts, and diagnostic histories taken by experienced clinicians. The team found that the psychological toll incurred was lower than NVVRS estimates, but still substantial: 18.7% of veterans developed PTSD during their lifetimes and 9.1% still suffered from the disorder as of 1990. The study also revealed that the more trauma exposure a veteran had experienced, the more likely he was to develop PTSD. An accompanying Perspective by R. J. McNally ( http://www.sciencemag.org/cgi/content/short/313/5789/923 ) highlighted the Report, and Dr. Dohrenwend discussed the findings in a segment of the 18 Aug *Science* podcast ( http://www.sciencemag.org/about/podcast.dtl#20060818 ). A related News Focus by G. Miller (http://www.sciencemag.org/cgi/content/short/313/5789/908 ) discussed current efforts to protect the mental health of U.S. troops in Iraq and Afghanistan.


Plant Peptides and Development

Because most plant cells are immobile, they communicate with each other through chemical signals. These mobile messages are especially important during development, when stem cells in the root and shoot tips (meristems) differentiate to form organized tissues. Two Reports in the 11 Aug 2006 *Science* described the isolation of two small peptides that fulfill such short-range signaling functions. Interestingly, both peptides are very similar in amino acid sequence but have counteracting functions. Kondo et al. ( http://www.sciencemag.org/cgi/content/short/313/5788/845 ) reported that a gene called *CLV3* encodes a 12-amino acid peptide that promotes stem cell differentiation during root and shoot development. And Ito et al. ( http://www.sciencemag.org/cgi/content/short/313/5788/842 ) found that a related 12-amino acid peptide inhibits the development of xylem (the principal water-conducting tissue in vascular plants) by suppressing differentiation of stem cells in the vascular system. The findings add to our understanding of the myriad signaling molecules and pathways that guide plant development. An accompanying Perspective by R. Simon and Y. Stahl ( http://www.sciencemag.org/cgi/content/short/313/5788/773 ) highlighted the Reports.


Controlling Gut Microbes

Mammals rely on a vast community of gut microbes to help process nutrients into usable forms and to keep pathogens at bay. In return, the gut offers these bacterial helpers a protected and nutrient-rich living environment. Maintaining the mutually beneficial nature of this relationship requires containment of resident microbes within the gut lumen, as they can wreak inflammatory havoc if they escape. Mammals use several adaptive and innate systems to keep gut flora in check, and a Report in the 25 Aug. 2006 *Science* revealed an addition to the repertoire. Cash et al. ( http://www.sciencemag.org/cgi/content/short/313/5790/1126 ) showed that specialized gut epithelial cells called Paneth cells produce a lectin (a carbohydrate-binding protein) that binds peptidoglycan on the surface of bacteria, and that this binding leads directly to bacterial killing. The preferential binding of the lectin to Gram-positive bacteria rather than the more predominant intestinal Gram-negative bacteria suggests that this protein may not only help regulate the mix of gut microbes, but may also eliminate potential pathogens that cannot be controlled by the resident gut flora alone. An accompanying Perspective by W. Strober ( http://www.sciencemag.org/cgi/content/short/313/5790/1052 ) highlighted the Report.


Explaining Tropical Diversity

Why are there so many species of insects in tropical forests relative to temperate ones? Is it because tropical forests boast greater tree diversity? Or does the disparity reflect differences in the number of plant species hosting each insect species (so-called host specificity)? Two studies reported in the 25 Aug 2006 issue of *Science* offered new insights into the complexities of plant-insect coevolution. Novotny et al. ( published online 13 Jul; http://www.sciencemag.org/cgi/content/short/313/5790/1115 ) compared temperate and tropical communities of herbivorous insects (in central Europe and Papua New Guinea, respectively) in phylogenetically comparable sets of local tree species. They found that tree species in both regions supported similar overall diversity of leaf-eating insect species per unit area of foliage. Instead, their analysis suggests that the richness of insect species in tropical forests is driven by plant diversity. However, a study of plant-herbivore diversity following extinction shows that this may not be a steadfast ecological rule. Wilf et al. ( http://www.sciencemag.org/cgi/content/short/313/5790/1112 ) examined thousands of fossil leaves dating back to the end-Cretaceous mass extinction event some 65.5 million years ago. Analysis of leaf diversity and signature types of leaf damage incurred by insects shows that plant and herbivore recovery following the extinction was both slow and patchy. Plants diversified without many insects in some places, whereas elsewhere herbivorous insects diversified despite few plant species. An accompanying Perspective by R. L. Kitching ( http://www.sciencemag.org/cgi/content/short/313/5790/1055 ) discussed the importance of these studies to our understanding of tropical ecology.


A Thirsty World
http://www.sciencemag.org/cgi/content/summary/313/5790/1067

Despite the fact that most of Earth’s surface is covered by oceans, the availability of fresh water remains a pressing concern throughout the world. In a special collection of articles in the 25 Aug 2006 issue, *Science* explored some of the scientific an engineering challenges to obtaining and maintaining a clean and plentiful water supply. Review articles discussed our current understanding of natural hydrological cycles and the water-quality problems caused by trace chemicals. Two Perspectives looked at ongoing efforts to combat waterborne infectious diseases and the multipronged strategy that Israel has adopted to procure fresh water in an arid environment. Accompanying News stories focused on resource issues specific to the Gaza region and the promise of new desalination technologies, and two related stories in the magazine’s News Focus section described ambitious engineering efforts in China and India to divert rivers and floodwaters to the countries’ driest areas. Finally, a related Editorial by Kennedy and Hanson underscored the importance of continued collaboration among scientists and policy makers to ensure effective water resource management.


Aerosols, Clouds, and Climate

Smoke and pollution aerosols have been shown to affect cloud microphysics, cloud reflection of sunlight into space, and the onset of precipitation. However, the net impact of these aerosols on climate remains highly uncertain because of limited observational information and the difficulty of simulating complex cloud processes in atmospheric models. In a study reported in the 4 Aug 2006 *Science* (published online 13 Jul), Kaufman and Koren ( http://www.sciencemag.org/cgi/content/short/313/5787/655 ) attempted to address these issues by introducing a new dimension of measurements to the mix. Using solar measurements taken at ground-based sites around the globe, the team showed that a higher concentration of aerosols in the air increases cloudiness, but that cloud coverage was negatively correlated with how much sunlight was absorbed by the aerosols. These findings were independent of both the type of aerosol and geographic location. Overall, the researchers estimate that smoke and pollution aerosols may increase cloud cover by up to 5%. An accompanying Perspective by F.-M. Bréon ( http://www.sciencemag.org/cgi/content/short/313/5787/623 ) highlighted the Report and the strong need to better understand and model the effect of aerosols and climate.


The Moon’s Mysterious Bulge

The far side of the Moon boasts an unusual bulge at the equator that has puzzled scientists for centuries. Researchers have proposed a number of explanations for the protuberance, but none seem to make sense given the present size and nearly circular shape of the lunar orbit. Now, a Report in the 4 Aug 2006 *Science* contends that an eccentric orbit in the moon’s distant past might be responsible for its peculiar shape. Garrick-Bethell et al. ( http://www.sciencemag.org/cgi/content/short/313/5787/652 ) modeled the Moon’s position and orbit as they existed millions of years ago by extrapolating back from ancient records of solar eclipses and changes in the distance between Earth and the Moon. They showed that the Moon’s shape can be explained if it had been in an eccentric orbit 100 million years after its formation, while it was beginning to solidify. If the Moon was spinning 1.5 times on its own axis for each time it orbited the Earth, instead of only once as it does now, it would have been spinning fast enough to stretch the cooling magma to form the "fossil bulge" seen today in the lunar gravity field. As noted in an accompanying Perspective by K. Innanen ( http://www.sciencemag.org/cgi/content/short/313/5787/622 ), "[t]his work should provide impetus for renewed analytical interest in the fascinating history of our still mysterious cosmic companion." A co-author of the study, Dr. Zuber, explained the lunar mystery in the 4 Aug podcast ( http://www.sciencemag.org/about/podcast.dtl#20060804 ).


Probing the Faintest Stars

When stars are born, they contract under gravity, increasing their central temperatures and densities. If a star is massive enough, its core will become hot enough to sustain hydrogen-burning nuclear fusion, allowing the star to shine for many billions of years. But if the star’s mass falls below a certain value, it will run out of nuclear fuel and the resulting so-called brown dwarf will fade away within a billion years. Nailing down this critical mass, known as the brown dwarf limit, has been difficult because the stars just above the limit are so dim. Now, thanks to 5 days of time on the Hubble Space Telescope, researchers have been able to probe the faintest stars in nearby globular star cluster NGC 6397. In a Research Article in the 18 Aug 2006 *Science*, Richer et al. ( http://www.sciencemag.org/cgi/content/short/313/5789/936 ) report that the lowest mass star capable of burning hydrogen is 0.083 times the mass of the sun -- a value that matches theoretical predictions. The team also reported that the cluster’s white dwarfs -- burnt-out remnants of stars that dim as they cool over time -- confirm another theoretical prediction: that they turn bluer as they age because hydrogen in their atmospheres absorb redder wavelengths of radiation. An accompanying News story by Y. Bhattacharjee ( http://www.sciencemag.org/cgi/content/short/313/5789/903a ) and a segment of the 18 Aug podcast ( http://www.sciencemag.org/about/podcast.dtl#20060818 ) highlighted the findings.


Etna Caught In the Act

Mount Etna, located on the island of Sicily, is one of the most active volcanoes in the world. In a Report in the 11 Aug 2006 *Science* Patanè et al. ( http://www.sciencemag.org/cgi/content/short/313/5788/821 ) offered a detailed seismic profile of Etna’s largest eruption in recent history, which look place over several months between 2002 and 2003 and was characterized by intense explosive activity with fire fountains and continuous fallout of volcanic ash and rock. Armed with seismic data recorded throughout large network of stations on and around Mt. Etna, the team used a technique called repeated seismic tomography to image spatial and temporal changes in the volume of volcanic rock and fluid. The method is analogous to a CAT scanning, which involves layering many "cross-sections" to create a three-dimensional image of the human body. The researchers observed major changes in the ratio of shear- and pressure-wave speed both prior to and during the eruption, and these changes correlated closely with magma movements within the volcano. Images also revealed the appearance of anomalous low-velocity zones that were indicative of rising gas-rich magma in the few months prior to the eruption. As noted in an accompanying Perspective by G. R. Foulger ( http://www.sciencemag.org/cgi/content/short/313/5788/768 ), further development of time-lapse seismic tomography should help to predict volcanic hazards at Mt. Etna and elsewhere in the future.


Smaller Pores Pack Punch

Electronic devices from laptop computers to cameras are starting to require more power than batteries can efficiently discharge. But these and many other gadgets also contain capacitors -- another type of energy-storage device that can deliver quick bursts of power. Although capacitors cannot store as much energy as batteries of the same size, so-called "supercapacitors" are beginning to close the gap. Unlike batteries, which release energy through electrochemical reactions, supercapacitors exploit the electrostatic separation between electrolyte ions and highly porous electrodes that are typically made of carbon. Standard thinking has been that larger pores are better because they increase the mobility of cations and anions. Now, results from a new study published online on *Science*Express on 17 Aug 2006 by Chmiola et al. ( http://www.sciencemag.org/cgi/content/abstract/1132195 ) challenge this notion. Using a method involving high-temperature chlorination of carbon compounds called metal carbides, the researchers were able to create carbon mesh materials with uniform pore sizes between 0.6 and 2.25 nanometers across. When they measured the energy-storing capabilities of these materials, they unexpectedly found that at pore sizes less than about 1 nanometer -- smaller than the size of electrolyte ions -- capacitance increased sharply. Exactly how ions manage to squeeze through such small spaces is puzzling, but the findings may nevertheless lead to a new generation of supercapacitors with even greater energy-storage potential. An accompanying News story by R. F. Service ( http://www.sciencemag.org/cgi/content/short/313/5789/902 ) in the 18 Aug issue highlighted the Report.

In Science’s Signal Transduction Knowledge Environment (STKE) 

A Metabolic Regulatory Network

Nutrients such as glucose and amino acids have traditionally been viewed as building blocks of macromolecules and as substrates for the generation of high-energy molecules such as adenosine triphosphate (ATP). However, these nutrients can also serve as important signaling molecules in complex, nutrient-sensing signaling pathways that regulate various aspects of fuel and energy metabolism and influence cell growth and proliferation. In a Review article published 1 Aug 2006 in *Science*’s Signal Transduction Knowledge Environment (STKE), S. Marshall ( http://stke.sciencemag.org/cgi/content/abstract/sigtrans;2006/346/re7 ) discussed three well-established nutrient signaling pathways -- the hexosamine signaling pathway, the mTOR (mammalian target of rapamycin) signaling pathway, and the adenosine monophosphate–activated protein kinase (AMPK) signaling pathway -- as components of a large "metabolic regulatory network" that has implications for diseases such as diabetes, obesity, and cancer. Understanding how nutrients control metabolism and how nutrient excess and/or hormone signaling defects influence pathogenesis should help facilitate the search for novel therapeutic compounds to prevent and treat these diseases.

Also in STKE this month:
--Dhanasekaran highlighted the newly discovered role of G protein in receptor tyrosine kinase signaling (8 Aug 2006; http://stke.sciencemag.org/cgi/content/abstract/sigtrans;2006/347/pe31)
--Heinemann and Hoshi looked at a potassium channel subunit that doubles as a redox enzyme (29 Aug 2006; http://stke.sciencemag.org/cgi/content/abstract/stke.3502006pe33 )
--Philip and Scarlata described methods for measuring protein affinities on membrane surfaces by fluorescence spectroscopy (29 Aug 2006; http://stke.sciencemag.org/cgi/content/abstract/stke.3502006pl5).