 This month in Science Roundup: Sponsored by:
  Changing OceansSpecial Issue Introduction The ocean is a dynamic and rapidly evolving environment. Some of the transformations that we see are ones we are causing, and some are new to us only because we are looking in greater detail and with more sophisticated tools. A special section of the 18 Jun 2010 Science highlighted some of the ways in which we see our oceans changing. Review articles discussed how eddies and wind affect ocean circulation, the growing human footprint on ocean chemistry, sea-level rise and its impact on coastal zones, and the effects of climate change on marine ecosystems. News articles, meanwhile, examined ocean acidification, increasing ocean noise due to ship traffic (listen to the related podcast interview), improvements in shrimp aquaculture, and the ocean's garbage patches. Science Careers profiled human geographer Joshua Cinner, whose work informs coral reef management. Also on the ocean front, an Editorial by Church discussed the importance of extending ocean-observing systems to cover a wider range of ocean properties and a Policy Forum by Lubchenco and Sutley proposed an approach to safeguard U.S. ocean, coastal, and Great Lakes ecosystems from the increasingly numerous and intense stresses that human activities are causing. Oxytocin and Intergroup Conflict Soldiers will risk their lives to defeat the enemy and protect their country during intergroup conflicts. This combination of self-sacrifice and aggression toward competing groups is known as parochial altruism. In the 11 Jun 2010 Science De Dreu et al. reported that this behavior is regulated by oxytocin -- a short peptide hormone that is produced in the hypothalamus and has been shown to promote social binding in a wide range of animals, including humans. In experiments with groups of undergraduate men playing a version of an economic game known as the prisoner's dilemma game, the researchers found that those who received a dose of oxytocin behaved more altruistically toward members of their own group. However, the participants also displayed more "defensive aggression" toward outsiders, preemptively punishing members of a competing group when their own group was in danger of suffering a financial loss (see the related News story by G. Miller). The results thus suggest that there may be a neurobiological basis for intergroup conflict in humans. In a related podcast segment, lead author Carsten De Dreu discussed the findings and Nir Halevy, a co-developer of the prisoner's dilemma game who was not involved in the study, provided additional commentary.  Engineered BreathingTwo papers reported in Science this month describe advances in biomedical engineering that may one day lead to the generation of fully functional lungs in the laboratory and provide alternative model systems for preliminary pharmaceutical and toxicology studies. --Petersen et al. (24 Jun 2010 in Science Express) reported that decellularized rat lungs rebuilt with new cells in vitro can function at a rudimentary level when implanted back into a rat. The team first removed all cells from a normal rat lung, leaving behind a scaffold that retained the organs' overall structure. The scaffold was then placed in a bioreactor along with a mixture of lung blood vessel and airway cells. After about a week of culture, an engineered lung was produced. When transplanted into rats for a short period of time, the engineered lungs were able to inflate with air and oxygenate blood. The results represent a promising initial step toward the ultimate goal of generating fully functional lungs in the laboratory (listen to the related podcast segment). A ScienceNOW story by M. Leslie included a video of the procedure and the working transplanted lungs. --Huh et al. (25 Jun 2010) created a microfluidic device that mimics the alveolar-capillary interface of the human lung and reproduces multiple physiological lung functions, including pathogen-induced inflammatory responses. Such "organ-on-a-chip" microdevices that can mimic the tissue-tissue interfaces critical to organ function may expand the capabilities of cell culture models and provide low-cost alternatives to animal and clinical studies for drug screening and toxicology applications. Warm-Blooded Reptiles? When dinosaurs roamed the land in the Mesozoic (251 to 65 million years ago), the top predators in the ocean were reptiles. In a Report in the 11 Jun 2010 Science, Bernard et al. investigated the metabolism in three lineages of these extinct marine reptiles -- ichthyosaurs, plesiosaurs, and mosasaurs -- by comparing the oxygen isotope compositions in their teeth, which depend both on body temperature and the composition of ingested water, with those of coexisting fish. The data imply that icthyosaurs and plesiosaurs, which were pursuit predators, were able to maintain a constant and high body temperature in oceanic environments ranging from tropical to cold temperature. The data for the mosasaurs, which are thought to have hunted by ambush, are more equivocal, but are consistent with the idea that these reptiles were able to control their body temperature to some degree. An accompanying Perspective by R. Motani noted that evolutionary triggers for homeothermy (maintenance of constant body temperature in different thermal environments) are generally difficult to decipher, but that "comparisons of the evolutionary records of marine reptiles and fish may illuminate common environmental factors." Origins of Oort Cloud Comets Long-period comets (comets with periods greater than 200 years) originate from the Oort cloud, a vast reservoir of icy bodies that surrounds the solar system. These bodies are thought to be remnants from the formation of the solar system and to have formed in the Sun's protoplanetary disk and then been ejected into orbit as the giant planets formed and evolved. Curiously, the Oort cloud appears to contain far more bodies than models would predict, leading researchers to explore an alternative hypothesis about the origins of Oort cloud comets -- namely, that they formed around other stars and were gravitationally captured by the Sun when it was still in its birth cluster. In a Report published online in Science Express on 10 Jun 2010, Levison et al. used detailed numerical simulations to investigate this possibility. Their simulations, integrating the orbits of a large number of comets and stars embedded in a spherically symmetric distribution of gas, suggest that a substantial fraction of Oort cloud comets, perhaps more than 90%, probably originated in the protoplanetary disks of other stars. Lead author Hal Levison discussed the work in further detail in a related podcast interview).  Crickets in the WildMost studies of insect behavior have been confined to the lab due to the technical challenges of monitoring these small creatures in the wild. Now, thanks to 24-hour video surveillance and DNA profiling, researchers have been able to track the lives of wild field crickets in unprecedented detail. As described in a Report in the 4 Jun 2010 Science, Rodríguez-Muñoz et al. tracked the members of a wild population of field crickets across two generations in order to better understand the factors that predict the reproductive success of males and females (listen to the related podcast interview with senior author Tom Tregenza). Their observations confirm the fundamental prediction that males vary more in their reproductive success than females. However, the team unexpectedly found that some factors that contribute to a male's success in gaining mates fail to predict reproductive success. For example, being the alpha cricket (or at least winning most of one's aggressive encounters) turns out not to guarantee having more offspring. A Perspective by M. Zuk highlighted the study and a related ScienceNOW story featured narrated video of field crickets in the act of mating, foraging, and falling victim to predators. Early Fractal Haze The atmosphere of the Archean Earth (3.8 to 2.5 billion years ago) was much different from the present one. The Sun is thought to have been 30% less luminous than today, yet the surface of the planet was warm enough to prevent glacier formation and for early life to become established. Why were temperatures so high, despite the lower flux of solar energy? In a Report in the 4 Jun 2010 Science, Wolf and Toon proposed that a photochemical haze in which organic aerosol particles aggregate and take on a fractal structure could be the reason. In such a layer, the smallest spherical aerosol particles would interact with shortwave radiation, while larger aggregate structures would affect longer wavelengths. The end result would be a haze that was opaque enough to block the ultraviolet radiation that would have hindered or prevented life from arising, but transparent enough in the visible and near-infrared wavelengths to keep the atmosphere warm. An accompanying Perspective by C.F. Chyba discussed how the new simulation results fit with theories about the composition of Earth's early atmosphere and the so-called "early faint Sun paradox." Stopping Sepsis Sepsis is a serious medical condition characterized by an uncontrolled inflammatory response to infection. Sepsis often results in tissue damage, organ failure and/or death, and current treatments are not very effective. In a Report in the 4 Jun 2010 Science, Puneet et al. provided compelling evidence that sphingosine kinase 1 (SphK1) -- an enzyme that resides in immune cells and is activated by inflammatory signals -- may represent an important therapeutic target for the treatment of sepsis (see the related Perspective by L.A.J. O'Neill in the 16 Jun issue of Science Translational Medicine). The researchers first showed that expression of SphK1 on human phagocytes (white blood cells that engulf harmful microbes and other foreign particles) increases in response to bacterial products and is also elevated in patients with severe sepsis. Blocking SphK1 expression by means of small interfering RNA, or inhibiting SphK1 enzymatic activity with a small-molecule chemical inhibitor, reduced systemic inflammation and lethal shock in two mouse models of sepsis. Protection was also seen when mice were treated with the SphK1 inhibitor up to 8 hours after sepsis induction, and this protection was enhanced if mice were given a broad-spectrum antibiotic. Senior author Alirio Melendez discussed the work in a related podcast segment.  Dating Ancient EgyptThe dynasties of ancient Egypt dominated the Mediterranean during the Bronze and Iron ages (the 3rd to 1st millennia B.C.E.). Historical chronologies for this period are based on abundant but fragmentary written sources and archaeological evidence, and various interpretations exist. Radiocarbon dating has the potential to verify these interpretations. In a Report in the 18 Jun 2010 Science, Bronk Ramsey et al. presented a comprehensive radiocarbon-based record of dynastic Egypt using measurements from 211 short-lived plant samples obtained from museum collections that were directly associated with particular reigns of ancient Egyptian kings. The team then used historical information about known reign order and length to obtain a detailed chronology. The new dates agree most closely with the previous older chronology, but force some revisions to the timing of events in the Old Kingdom -- the period in the 3rd millennium B.C.E. when Egypt attained its first continuous peak of civilization. The researchers note that their record "has implications for the wider Mediterranean and surrounding regions that rely on linkages to Egypt to anchor their own chronologies." H.J. Bruins expanded on this topic in an accompanying Perspective. Space in the Brain Space is represented in the brain by a complex circuitry of multiple cell types, which form a collective dynamic representation of our position as we move through the environment. Whether we are born with the ability to represent space, or if it is a result of learning from experience, has been a mystery. Two Reports in the 18 Jun 2010 Science now provide support for the view that the animal brain is able to represent space without prior experience of exploring a location (see the related Perspective by L. Palmer and G. Lynch). Wills et al. and Langston et al. investigated the early development of spatial activity in rat pups as they began to explore their environment. In both studies, the researchers placed electrodes in the hippocampal formation of 2-week-old rat pups and recorded the activity of individual neurons 2 days later, when the pups opened their eyes for the first time, and for 2 weeks afterward. Both studies agree that direction cells, which fire when the animal's head points in a particular direction in relation to the environment, and place cells, which fire when the animal moves through a particular location, were both already present by the time the rat pups left their nest for the first time. The studies disagree about the appearance of the third class of spatial neurons, the grid cells, which fire at the vertices of a regular, repeating grid that covers the environment. Despite this disagreement, overall, the results provide evidence that spatial representation indeed includes an innate component prior to experience. Photoemission Delay When a high-energy photon hits an atom and is absorbed, the result can be the excitation and emission of an electron. This photoemission process is generally assumed to occur instantaneously, and represents the definition of "time-zero" in clocking similar atomic-scale events. Now, in a Research Article in the 25 Jun 2010 Science, Schultze et al. have used ultrafast spectroscopy, with light pulses on the time scale of several tens of attoseconds, to test this assumption directly. The team measured the photoemission of electrons from neon atoms bombarded with 100–electron volt light pulses and found a 20-attosecond time delay between the emission of electrons from different atomic orbitals. This very short delay may eventually help scientists constrain a more precise "time -zero" down to just a few attoseconds. An accompanying Perspective by H.W. van der Hart noted that "[t]his finding not only allows further studies of the timing of photoemission but also provides a new way to investigate electron interactions in atoms." In Science Signaling
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