Science Roundup


This month’s Science Roundup is sponsored by Qiagen
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Diversification and Speciation
Special Online Collection

In the 6 Feb 2009 issue, Science continued its celebration of the 200th birthday of Charles Darwin. In a special section on the speciation of living organisms, five Reviews presented multiple views on diversification at scales ranging from the macroevolutionary to the molecular. Topics included the extents to which biotic and abiotic factors have shaped species diversity in the fossil record, patterns of adaptive radiation, microbial species formation, and predictive principles of genetic evolution. Elsewhere in the magazine, the second in a series of monthly "origins" essays discussed the origins of art and symbolic behavior (listen to the related podcast interview), the Commentary section featured reviews of new books about evolution, an Editorial highlighted uncertainties in our estimates of the world’s living species, and research papers covered themes from mass extinction to conservation and hybrid sterility. Online, Science Careers offered a feature on researchers in the museum world, who play a vital role in evolutionary research.


Color and Cognition

Color is a fundamental aspect of human perception, and its effects on cognition and behavior have intrigued generations of researchers. Previous research on how color affects cognition, however, has yielded inconsistent findings. For example, some research suggests that red enhances cognitive task performance as compared with blue or green, while other studies suggest the opposite. In a Report in the 27 Feb 2008 Science (published online 5 Feb), Mehta and Zhu sought to reconcile this inconsistency (see the ScienceNOW story by G. Miller). In a series of experiments, the researchers manipulated the background color on a computer screen while volunteers performed a variety of tasks. For those tasks that required attention to detail -- such as recalling words from a list or proofreading addresses -- participants performed better when the background was red, as opposed to blue or neutral. Blue, on the other hand, stimulated creativity. When subjects were asked to name as many uses for a brick as they could think of in a minute, they came up with more creative responses and earned higher creativity scores from a jury of their peers when the background was blue. The researchers surmise that the results reflect the different associations conjured by red and blue. Red often alerts us to danger or mistakes, signaling the need to be vigilant. In contrast, blue is often associated with peace and tranquility, which may put people in a more creative mindset.


Envy and Schadenfreude in the Brain

Neurocientists have identified the neural systems responsible for experiences of physical pain and pleasure. The pain network consists primarily of the dorsal anterior cingulate cortex (dACC), insula, and somatosensory cortex, whereas the reward or pleasure network consists of the neural structures receiving the neurostransmitter dopamine from the ventral tegmental area, including the ventral striatum, ventromedial prefrontal cortex, and the amygdala. Now, in a Report in the 13 Feb 2009 Science, Takahashi et al. show that social pains and pleasures involve these same circuitries. Using functional magnetic resonance imaging, the researchers tracked the neural responses of healthy human subjects in situations designed to invoke feelings of envy and schadenfreude (pleasure from someone else’s misfortune). They found that envy correlated with activation of the dACC, where physical pain and cognitive conflicts are processed, and that stronger envy (felt when the envied person had superior or more self-relevant characteristics) induced stronger activation. In contrast, schadenfreude was associated with activation of the ventral striatum, a central node of reward processing, and activation of this region was more intense when misfortune befell an envied person rather than a neutral person. An accompanying Perspective by M.D. Lieberman and N.I. Eisenberger noted that "[t]he link between social and physical pains and pleasures adds to the growing chorus of neurocognitive findings that point to the critical importance of the social world for the surviving and thriving of humans."


Ancestral Viral Integration

Many species of parasitic wasp inject virus-like particles called polydnaviruses (PDVs) into their caterpillar hosts, paralyzing host defenses and allowing their own eggs to survive and develop. Curiously, polydnavirus DNA encodes virtually none of the structural proteins needed for viruses to replicate, raising questions about whether PDVs are actually of viral origin. A Report in the 13 Feb 2009 Science now resolves this genetic mystery. Bezier et al. analyzed DNA derived from wasp ovaries, where PDVs are produced, and identified 22 genes closely related to those of insect viruses called nudiviruses -- a sister group of baculoviruses. These genes encode subunits of a viral RNA polymerase and proteins involved in polydnavirus particle assembly and packaging. Conservation of this viral machinery in related wasp lineages suggests that nudiviruses infected wasps a few million years ago and that, over time, the viral DNA fully integrated into the wasp genome (see the related ScienceNOW story by R. Zelkowitz). Today, the wasps and the polydnaviruses need each other to survive. An accompanying Perspective by D.B. Stolz and J.B. Whitfield noted that "there is now reason to start thinking about virus-host relationships in much broader terms."


Early Hominin Footprints

The human foot -- composed of twenty-six bones held in a three-dimensional latticework of ligaments and tendons -- is one of our more distinctive adaptations. Preserved footprints can provide important information about when and how our foot structure and bipedal gait evolved, but research has been hampered by a scarcity of prints and an inadequate hominin fossil record. Now, in a Report in the 27 Feb 2009 Science, Bennett et al. report the discovery of a ~1.5 million-year-old fossil footprint trail at Ileret, east of Lake Turkana in Kenya -- the oldest attributable to our own genus, Homo. Analysis of the footprint surfaces by laser scanning and geometric morphometric statistical techniques reveal that the size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and that the prints are morphologically distinct from the 3.75-million-year-old footprints recovered 30 years ago from Laetoli, Tanzania and attributed to Australopithecus afarensis. The Ileret footprints show the hallmarks of a relatively modern human-like foot including a medial arch, an adducted (in-line) big toe, and evidence of the transfer of weight to the ball of the foot before toe push-off. A related Perspective by R. H. Crompton and T. C. Pataky commented that the new findings "herald an exciting time for studies of the evolution of human gait."


Phytoplankton Trapping

Phytoplankton -- the microscopic photosynthetic organisms at the base of oceanic food webs -- play a key role in the ecology of our planet. Although many species are active swimmers, phytoplankton are also known to aggregate into dense layers millimeters to meters in thickness that can extend horizontally for kilometers below the ocean surface. The concentrated plankton and detritus in these layers provide sustenance for zooplankton and fish larvae, but they can also contain toxic phytoplankton species that seed harmful algal blooms. In a Report in the 20 Feb 2009 Science, Durham et al. proposed a mechanism by which plankton layers form, which they term "gyrotactic trapping." The team explains that many phytoplankton species swim upward against gravity, but that this migration can be disrupted by a discontinuity, or shear, in water flow. They demonstrated that when the shear exceeds a critical value, the cells’ orientation machinery fails, causing them to spin continuously. Halted by this pattern of nondirectional movement, the plankton accumulate in layers. Given the wide range of environments and species associated with phytoplankton layers, it is unlikely that a single mechanism is responsible for the formation of all layers. Nevertheless, these results show that the microscopic coupling between microorganism motility and ambient fluid motion can shape macroscopic features of the marine ecological landscape. An accompanying Perspective by D. Grünbaum highlighted the study.


Forming Oceanic Crust

Nearly two-thirds of Earth’s crust is formed at mid-ocean ridges. The crust can be roughly dated using magnetic signatures (magnetic minerals in the crust are magnetized in the direction of Earth’s magnetic field as they cool and solidify), but details about the mechanism(s) of crustal accretion have been difficult to discern. In the 20 Feb 2009 Science, Lissenberg et al.  reported that tiny zircon crystals that are relatively abundant in the oceanic crust make it easy to date the crust, thereby providing a clearer picture of the formation processes involved. The team performed high-precision uranium-lead dating on zircon grains found in rock layers on the mid-Atlantic ridge. Their data reveal a systematic increase in zircon age away from the center of the ridge, which indicates that the crust grew in a slow and regular pattern, at least at that location. Each sample had single-grain zircon dates that span 90,000 to 235,000 years, which the researchers interpret to reflect the time scale of zircon crystallization and thus the cooling rate of the crust. An accompanying Perspective by P.J. Michael and M.J. Cheadle highlighted the Report, noting that "[a]ccurate cooling rates will place constraints on how oceanic crust grows and may even help to constrain how deep hydrothermal circulation might go."


SELENE and the Lunar Farside

The Moon is our closest planetary neighbor, but many questions about its origin and early history remain unanswered. Particularly confounding are the notable differences in crustal thickness and density, composition, and volcanic activity between the Moon’s nearside and its farside. In the 13 Feb 2009 issue, four Reports presented observations from the Japanese Selenological and Engineering Explorer (SELENE or Kaguya) mission that further our understanding of the Moon’s evolution and, in particular, of its farside. Using data from a laser altimeter on board the explorer, Araki et al.  derived a high-resolution lunar topographic map. Spectral analysis of the topography indicates that the Moon has a dry, rigid crust. Namiki et al.  provided an improved gravity map of the Moon, which shows a marked difference between the nearside and farside. By analyzing images taken by the SELENE Terrain Camera, Haruyama et al. determined that volcanism on the lunar farside lasted about 500 millions years longer than previously thought. And Ono et al. described subsurface stratifications on the lunar nearside, which indicate a possible period of reduced volcanism in its early history. G. A. Neumann and E. Mazarico discussed the findings in a related Perspective and podcast interview.


From Greenhouse to Icehouse

For much of Earth’s history, the climate has been considerably warmer than it is today. But about 34 million years ago, at the Eocene-Oligocene transition, Earth’s climate underwent a dramatic shift from a relatively ice-free world to one in which Antarctica became buried beneath kilometers of ice. In a Report in the 27 Feb 2009 Science, Liu et al. shed light on how Earth’s temperature changed during this transition. Geochemical evidence of sea surface temperature changes at ocean locations around the world indicate that mid-to-high-latitude surface waters cooled from about 20 degrees to 15 degrees Celsius. Although lower latitudes also experienced cooling, the effect was not as significant. Combining these results with oxygen isotopic data -- which can be used to estimate ice volume as well as temperature -- indicates that the volume of continental ice varied only slightly during the transition, and that contrary to a previous analysis, glaciation of the Northern Hemisphere did not occur. An accompanying Perspective by L. R. Kump considered how a reduction in atmospheric carbon dioxide concentrations could explain the cooling patterns indicated by the new temperature proxies.


A Better Barrier?

Plastics are versatile, easy to manufacture, and relatively inexpensive, making them successful replacements for more traditional materials such as glass, metals, and wood. In applications such as packaging, however, molded plastics can be a disadvantage because they are permeable to atmospheric gases -- a property that can compromise the integrity of products from beer to intricate electronics. In a Report in the 6 Feb 2009 Science, Wang et al. reported that a specialized crystallization process can cause commonly used polymers to form so called polymer single crystals that show a marked reduction in gas permeability. The researchers made a series of polymer films through a multiple folding process generating extremely thin, alternating layers of two different polymers: polyethylene oxide or PEO -- a crystallizable polymer-- and ethylene-co-acrylic acid. They found that confining the thickness to 20 nanometers, forces the long-chain molecules of PEO into their most compact arrangement, that of large single crystals. The permeability of PEO to oxygen decreased by about two orders of magnitude in this crystalline form. The technique could thus aid the development of improved protective films and packaging materials. An accompanying Perspective by P.J. Lemstra highlighted the study.


New Route to Nanoelectronics

In the nascent days of the electronics industry, researchers would glue materials together by hand to develop new device structures. Electronics are growing ever smaller, however, and today it is possible to sandwich oxide materials together with atomic-scale precision, giving rise to insulating, metallic, and even superconducting behavior at their interfaces. Until now, fabrication of such metal oxide devices has required complex lithographic processes. Now, in a Research Article in the 20 Feb 2009 Science, Cen et al. have described a simpler approach. Using the tip of a conducting atomic force microscope, the team was able to etch tiny tunnel junctions and field-effect transistors -- as small as 2 nanometers across -- at the interface of lanthanum aluminate and strontium titanate (a polar and nonpolar semiconducting oxide, respectively). Moreover, these structures can be written and erased hundreds of times simply by scanning with a negative voltage or by illuminating with light. An accompanying Perspective by Reiner et al. noted that "[a]s the relation between structure and behavior is understood for more complicated materials systems, the number of potential applications will increase dramatically." Possible applications include environmental energy harvesting, thermoelectric energy conversion, memory-storage devices, chemical sensors, and more advanced logic circuits.


Brevia Highlights

The month in Science’s Brevia section:
-- Mitrovica et al. (6 Feb 2009) offered revised projections of sea-level rise caused by melting of the West Antarctic Ice Sheet that indicate accentuated rise in the oceans bordering North America and in the Indian Ocean.
-- Stutchbury et al. (13 Feb 2009) described how miniature recorders mounted on purple martins and wood thrush allow mapping of bird migration routes between North America and the Neotropics (see the related ScienceNOW story by J. Grom)
-- Evans and Reimer (20 Feb 2009) analyzed how open access to scientific research papers influences global participation in science and found that making articles available free online increases the rate at which they are cited, especially by authors in poorer countries.
-- Antonakis and Dalgas (27 Feb 2009) found that voters in political elections do not appropriately weight performance-based information on the candidates, but rather seem to use the same cues that children use to categorize individuals on competency.



In Science Signaling

ATP in the Immune System

Extracellular adenosine 5’-triphosphate (eATP) is widely used for cell-to-cell communication. The low concentration of eATP that exists in a "halo" surrounding resting cells signals the presence of neighboring living cells. Transient increases are used for basic physiological signaling in the nervous and vascular systems, whereas larger increases in eATP that are associated with cell death serve as a key "danger" signal in inflammatory processes. In a Perspective in the 3 Feb 2009 issue, A. Trautmann  highlighted two new studies that point to roles for ATP in the immune system. One group found that eATP provides a costimulatory signal to T cells to facilitate antigen recognition; another reported that ATP released by commensal bacteria drives the differentiation of intestinal T helper cells, which are involved in mediating an inflammatory response against infectious agents. The cellular networks responsible for these phenomena are still to be discovered.

Also in Science Signaling this month:
-- Kino et al. found that the guanine nucleotide exchange factor Brx is essential for osmotic stress–mediated expression of nfat5 (which encodes a key regulator of osmotic response) in lymphocytes (10 Feb 2009)
-- Inoue et al. showed that the cytoplasmic protein Dok-7 is required for the full activation of the muscle-specific receptor tyrosine kinase MuSK, which orchestrates the formation of neuromuscular junctions (24 Feb 2009)
-- Y. Cao discussed the effects of placental growth factor (PlGF) and VEGF-B, two vascular endothelial growth factors, on angiogenesis (24 Feb 2009)



This month’s Science Roundup is sponsored by Qiagen
NEW: QIAgility Rotor-Gene Q
Automated solutions for quantitative PCR
www.qiagen.com/goto/QIAgilityS



Image credits (in order of appearance): Science cover, 6 February 2009; Takahashi et al., Science 323, 937 (2009); Matthew Bennett/ Bournemouth University; Science cover, 13 February 2009.