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<jats:title>Lingering Atmospheric Perturbations</jats:title> <jats:p> Nitrous oxide and methane are chemically active greenhouse gases whose atmospheric abundances are greatly influenced by anthropogenic emissions. <jats:bold>Prather and Hsu</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="952" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196285">952</jats:related-article> ) used an atmospheric chemistry model to show how nitrous oxide emissions lower the concentration of tropospheric methane through a chain of chemical reactions that include stratospheric ozone depletion, changes in solar ultraviolet radiation fluxes, altered fluxes of ozone transport from the stratosphere to the troposphere, and increases in the amount of tropospheric hydroxyl radicals. This mechanism acts on a 108-year-long time scale—10 times longer than the atmospheric residence time of methane. </jats:p>

<jats:title>Feather of the Penguin</jats:title> <jats:p> Penguins are highly adapted for their cold, aquatic environment. Changes in their wings and feathers have allowed rapid swimming and protection from the near-freezing water. <jats:bold> Clarke <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="954" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193604">954</jats:related-article> , published online 30 September; see the cover) describe an early penguin, dating to about 35 million years ago, that includes well-preserved feathers. The melanosomes in the feathers, which influence their strength, as well as their color, are like those of many other aquatic birds and unlike those of present-day penguins, even though the morphology of the wings and feathers had already been modified. Thus, in penguins, the shape and form of the feather evolved before microstructural changes occurred. The melanosome arrangement also suggests that the penguin was mostly gray-brown. </jats:p>

<jats:title>Hot Tropical Explosion</jats:title> <jats:p> The Paleocene-Eocene Thermal Maximum (PETM), 55 million years ago, was a unique episode of rapid global warming (∼5°C), often used as an ancient analog for future global climate change. Climate alteration during the PETM has been extensively studied in the marine realm, and from a few temperate to polar terrestrial localities, but little is known about how the tropics responded to the high temperatures and high levels of CO <jats:sub>2</jats:sub> . Using evidence from pollen analysis, <jats:bold> Jaramillo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="957" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193833">957</jats:related-article> ) show that rapid tropical forest diversification occurred during the PETM, without plant extinction or regional aridity. Unexpectedly, diversity seemed to increase at higher temperatures, contradicting previous assumptions that tropical flora will succumb if temperatures become excessive. </jats:p>

<jats:title>Pulling Together</jats:title> <jats:p> Human social norms can be explored in experiments that provide insights into the situational conditions and individual preferences that prompt the expression of cooperative behavior and the enforcement of norms. <jats:bold> Rustagi <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="961" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193649">961</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6006" page="923" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198349">Vollan and Ostrom</jats:related-article> </jats:bold> ) analyzed a set of 49 user groups, comprising 679 individuals, who had been given the authority and responsibility to manage forests in the Bale region of Ethiopia. The forests managed by groups with larger proportions of conditional cooperators—that is, individuals who will behave in a cooperative fashion if others do so as well—produced more potential crop trees per hectare. Enforcing such behavior, via patrolling of the forests, which although a costly and time-intensive activity, was the key to productivity </jats:p>

<jats:title>River Food Chains</jats:title> <jats:p> Food chain length, or the number of organisms involved in any eat-or-be-eaten relationship, is a key property of aquatic habitats that regulates nutrient cycling, energy flow, and carbon exchange between aquatic ecosystems and the atmosphere. Investigating river food webs in North American watersheds, <jats:bold> Sabo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="965" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196005">965</jats:related-article> , published online 14 October) found discharge variation governed the link between ecosystem size (watershed area) and food chain length. River-drying truncated food chain length because intermittent streams have much higher discharge variation than perennial rivers. These results could be important for the management of rivers as drought and climate change may increase the frequency of river drying and discharge variability. </jats:p>

<jats:title>Fungal Invasion or Pollination?</jats:title> <jats:p> When pollen finds a compatible flower, it grows a pollen tube which must find the egg cell and release the sperm it carries. In searching for genes that affect pollen tubes in <jats:italic>Arabidopsis</jats:italic> , <jats:bold> Kessler <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="968" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195211">968</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6006" page="922" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198347"> <jats:bold>Govers and Angenent</jats:bold> </jats:related-article> ) found a gene previously implicated in susceptibility to powdery mildew infection (the <jats:italic>NTA</jats:italic> gene). The <jats:italic>NTA</jats:italic> gene encodes a seven-pass transmembrane protein, which, in combination with a receptor-like kinase called Fer, is needed for successful pollen tube growth; both sets of proteins are also needed for successful powdery mildew invasion. These processes hence share common mechanisms of cell invasion, but where they diverge is in the outcome: embryogenesis or pathogenesis. </jats:p>

<jats:title>A Steady Beat</jats:title> <jats:p> A regular heartbeat depends on steady function of the cardiac pacemaker. The early embryonic heart is neither as steady nor as organized as the mature heart. <jats:bold> Arrenberg <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="971" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195929">971</jats:related-article> ) used zebrafish engineered to express light-sensitive proteins to locate and manipulate the function of the cardiac pacemaker. By controlling the activity of small patches of cells with light beams, the authors monitored the development of the young heart, showing how the cardiac pacemaker develops during embryogenesis. </jats:p>

<jats:title>Reciprocal Regulation</jats:title> <jats:p> An essential step in many signaling cascades is inositol lipid hydrolysis catalyzed by phospholipase C–β. The latter is activated by the α subunit of the heterotrimeric G protein Gq, and it in turn inactivates Gαq, thus sharpening the signal. <jats:bold> Waldo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="974" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193438">974</jats:related-article> , published online 21 October) report structural and biochemical data that explain the basis of this reciprocal regulation. One domain of phospholipase C–β binds to activated Gαq. Though the phospholipase C–β active site remains occluded in the structure, the plug is probably removed upon G protein–dependent orientation of the lipase at the membrane. A second domain of phospholipase C–β accelerates guanosine triphosphate hydrolysis by Gαq causing the signaling complex to dissociate. </jats:p>

<jats:title>Infectious Amyloid?</jats:title> <jats:p> Patients with Alzheimer's disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimer's disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. <jats:bold> Eisele <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="980" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194516">980</jats:related-article> , published online 21 October; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6006" page="918" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1198314">Kim and Holtzman</jats:related-article> </jats:bold> ) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. </jats:p>

<jats:title>Coughing Back</jats:title> <jats:p> Resurgence of whooping cough (or pertussis) is problematic because of the risk of infant fatality, but it has been occurring despite the availability of a vaccine. Data from Sweden, where national vaccination for whooping cough was discontinued for 17 years, before resumption in 1996, was used by <jats:bold> Rohani <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="982" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194134">982</jats:related-article> ) to build a model that showed that age-specific social contacts were an important influence on the spread of infection. The model helped to explain why resumption of vaccination was so successful in curbing infant whooping cough but had no effect on pertussis in adolescents. The model thus demonstrated how potentially important it is to take account of age-stratification in a population when considering public health policy. </jats:p>