New and Exciting in PLoS this week

Busy with ScienceOnline2010 I did not have time to check out the new articles in PLoS ONE and other PLoS titles. Finally I found some time today, and here are my picks from the past few days. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. There are my own picks for the week – you go and look for your own favourites:


Moonlight Makes Owls More Chatty:

Lunar cycles seem to affect many of the rhythms, temporal patterns and behaviors of living things on Earth. Ambient light is known to affect visual communication in animals, with the conspicuousness of visual signals being largely determined by the light available for reflection by the sender. Although most previous studies in this context have focused on diurnal light, moonlight should not be neglected from the perspective of visual communication among nocturnal species. We recently discovered that eagle owls Bubo bubo communicate with conspecifics using a patch of white throat plumage that is repeatedly exposed during each call and is only visible during vocal displays. Here we provide evidence that this species uses moonlight to increase the conspicuousness of this visual signal during call displays. We found that call displays are directly influenced by the amount of moonlight, with silent nights being more frequent during periods with no-moonlight than moonlight. Furthermore, high numbers of calling bouts were more frequent at moonlight. Finally, call posts were located on higher positions on moonlit nights. Our results support the idea that moon phase affects the visual signaling behavior of this species, and provide a starting point for examination of this method of communication by nocturnal species.

The Advantages of a Tapered Whisker:

The role of facial vibrissae (whiskers) in the behavior of terrestrial mammals is principally as a supplement or substitute for short-distance vision. Each whisker in the array functions as a mechanical transducer, conveying forces applied along the shaft to mechanoreceptors in the follicle at the whisker base. Subsequent processing of mechanoreceptor output in the trigeminal nucleus and somatosensory cortex allows high accuracy discriminations of object distance, direction, and surface texture. The whiskers of terrestrial mammals are tapered and approximately circular in cross section. We characterize the taper of whiskers in nine mammal species, measure the mechanical deflection of isolated felid whiskers, and discuss the mechanics of a single whisker under static and oscillatory deflections. We argue that a tapered whisker provides some advantages for tactile perception (as compared to a hypothetical untapered whisker), and that this may explain why the taper has been preserved during the evolution of terrestrial mammals.

Democrats and Republicans Can Be Differentiated from Their Faces:

Individuals’ faces communicate a great deal of information about them. Although some of this information tends to be perceptually obvious (such as race and sex), much of it is perceptually ambiguous, without clear or obvious visual cues. Here we found that individuals’ political affiliations could be accurately discerned from their faces. In Study 1, perceivers were able to accurately distinguish whether U.S. Senate candidates were either Democrats or Republicans based on photos of their faces. Study 2 showed that these effects extended to Democrat and Republican college students, based on their senior yearbook photos. Study 3 then showed that these judgments were related to differences in perceived traits among the Democrat and Republican faces. Republicans were perceived as more powerful than Democrats. Moreover, as individual targets were perceived to be more powerful, they were more likely to be perceived as Republicans by others. Similarly, as individual targets were perceived to be warmer, they were more likely to be perceived as Democrats. These data suggest that perceivers’ beliefs about who is a Democrat and Republican may be based on perceptions of traits stereotypically associated with the two political parties and that, indeed, the guidance of these stereotypes may lead to categorizations of others’ political affiliations at rates significantly more accurate than chance guessing.

Genetic Variation at Nuclear Loci Fails to Distinguish Two Morphologically Distinct Species of Aquilegia:

Aquilegia formosa and pubescens are two closely related species belonging to the columbine genus. Despite their morphological and ecological differences, previous studies have revealed a large degree of intercompatibility, as well as little sequence divergence between these two taxa [1], [2]. We compared the inter- and intraspecific patterns of variation for 9 nuclear loci, and found that the two species were practically indistinguishable at the level of DNA sequence polymorphism, indicating either very recent speciation or continued gene flow. As a comparison, we also analyzed variation at two loci across 30 other Aquilegia taxa; this revealed slightly more differentiation among taxa, which seemed best explained by geographic distance. By contrast, we found no evidence for isolation by distance on a more local geographic scale. We conclude that the extremely low levels of genetic differentiation between A. formosa and A.pubescens at neutral loci will facilitate future genome-wide scans for speciation genes.

Insertion and Deletion Processes in Recent Human History:

Although insertions and deletions (indels) account for a sizable portion of genetic changes within and among species, they have received little attention because they are difficult to type, are alignment dependent and their underlying mutational process is poorly understood. A fundamental question in this respect is whether insertions and deletions are governed by similar or different processes and, if so, what these differences are. We use published resequencing data from Seattle SNPs and NIEHS human polymorphism databases to construct a genomewide data set of short polymorphic insertions and deletions in the human genome (n = 6228). We contrast these patterns of polymorphism with insertions and deletions fixed in the same regions since the divergence of human and chimpanzee (n = 10546). The macaque genome is used to resolve all indels into insertions and deletions. We find that the ratio of deletions to insertions is greater within humans than between human and chimpanzee. Deletions segregate at lower frequency in humans, providing evidence for deletions being under stronger purifying selection than insertions. The insertion and deletion rates correlate with several genomic features and we find evidence that both insertions and deletions are associated with point mutations. Finally, we find no evidence for a direct effect of the local recombination rate on the insertion and deletion rate. Our data strongly suggest that deletions are more deleterious than insertions but that insertions and deletions are otherwise generally governed by the same genomic factors.

The ‘Island Rule’ and Deep-Sea Gastropods: Re-Examining the Evidence:

One of the most intriguing patterns in mammalian biogeography is the “island rule”, which states that colonising species have a tendency to converge in body size, with larger species evolving decreased sizes and smaller species increased sizes. It has recently been suggested that an analogous pattern holds for the colonisation of the deep-sea benthos by marine Gastropoda. In particular, a pioneering study showed that gastropods from the Western Atlantic showed the same graded trend from dwarfism to gigantism that is evident in island endemic mammals. However, subsequent to the publication of the gastropod study, the standard tests of the island rule have been shown to yield false positives at a very high rate, leaving the result open to doubt. The evolution of gastropod body size in the deep sea is reexamined. Using an extended and updated data set, and improved statistical methods, it is shown that some results of the previous study may have been artifactual, but that its central conclusion is robust. It is further shown that the effect is not restricted to a single gastropod clade, that its strength increases markedly with depth, but that it applies even in the mesopelagic zone. The replication of the island rule in a distant taxonomic group and a partially analogous ecological situation could help to uncover the causes of the patterns observed–which are currently much disputed. The gastropod pattern is evident at intermediate depths, and so cannot be attributed to the unique features of abyssal ecology.

Language Structure Is Partly Determined by Social Structure:

Languages differ greatly both in their syntactic and morphological systems and in the social environments in which they exist. We challenge the view that language grammars are unrelated to social environments in which they are learned and used. We conducted a statistical analysis of >2,000 languages using a combination of demographic sources and the World Atlas of Language Structures– a database of structural language properties. We found strong relationships between linguistic factors related to morphological complexity, and demographic/socio-historical factors such as the number of language users, geographic spread, and degree of language contact. The analyses suggest that languages spoken by large groups have simpler inflectional morphology than languages spoken by smaller groups as measured on a variety of factors such as case systems and complexity of conjugations. Additionally, languages spoken by large groups are much more likely to use lexical strategies in place of inflectional morphology to encode evidentiality, negation, aspect, and possession. Our findings indicate that just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. As adults learn a language, features that are difficult for them to acquire, are less likely to be passed on to subsequent learners. Languages used for communication in large groups that include adult learners appear to have been subjected to such selection. Conversely, the morphological complexity common to languages used in small groups increases redundancy which may facilitate language learning by infants. We hypothesize that language structures are subjected to different evolutionary pressures in different social environments. Just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. The proposed Linguistic Niche Hypothesis has implications for answering the broad question of why languages differ in the way they do and makes empirical predictions regarding language acquisition capacities of children versus adults.

Generation, Purification and Transplantation of Photoreceptors Derived from Human Induced Pluripotent Stem Cells:

Inherited and acquired retinal degenerations are frequent causes of visual impairment and photoreceptor cell replacement therapy may restore visual function to these individuals. To provide a source of new retinal neurons for cell based therapies, we developed methods to derive retinal progenitors from human ES cells. In this report we have used a similar method to direct induced pluripotent stem cells (iPS) from human fibroblasts to a retinal progenitor fate, competent to generate photoreceptors. We also found we could purify the photoreceptors derived from the iPS cells using fluorescence activated cell sorting (FACS) after labeling photoreceptors with a lentivirus driving GFP from the IRBP cis-regulatory sequences. Moreover, we found that when we transplanted the FACS purified iPSC derived photoreceptors, they were able to integrate into a normal mouse retina and express photoreceptor markers. This report provides evidence that enriched populations of human photoreceptors can be derived from iPS cells.

Athlete Atypicity on the Edge of Human Achievement: Performances Stagnate after the Last Peak, in 1988:

The growth law for the development of top athletes performances remains unknown in quantifiable sport events. Here we present a growth model for 41351 best performers from 70 track and field (T&F) and swimming events and detail their characteristics over the modern Olympic era. We show that 64% of T&F events no longer improved since 1993, while 47% of swimming events stagnated after 1990, prior to a second progression step starting in 2000. Since then, 100% of swimming events continued to progress. We also provide a measurement of the atypicity for the 3919 best performances (BP) of each year in every event. The secular evolution of this parameter for T&F reveals four peaks; the most recent (1988) followed by a major stagnation. This last peak may correspond to the most recent successful attempt to push forward human physiological limits. No atypicity trend is detected in swimming. The upcoming rarefaction of new records in sport may be delayed by technological innovations, themselves depending upon economical constraints.

Sexual Seroadaptation: Lessons for Prevention and Sex Research from a Cohort of HIV-Positive Men Who Have Sex with Men:

Surveillance data on sexually transmitted infections (STIs) and behavioral characteristics identified in studies of the risk of seroconversion are often used as to track sexual behaviors that spread HIV. However, such analyses can be confounded by “seroadaptation”–the restriction of unprotected anal intercourse (UAI), especially unprotected insertive UAI, to seroconcordant partnerships. We utilized sexual network methodology and repeated-measures statistics to test the hypothesis that seroadaptive strategies reduce the risk of HIV transmission despite numerous partnerships and frequent UAI. In a prospective cohort study of HIV superinfection including 168 HIV-positive men who have sex with men (MSM), we found extensive seroadaptation. UAI was 15.5 times more likely to occur with a positive partner than a negative one (95% confidence interval [CI], 9.1-26.4). Receptive UAI was 4.3 times more likely in seroconcordant partnerships than with negative partners (95% CI, 2.8-6.6), but insertive UAI was 13.6 times more likely with positives (95% CI, 7.2-25.6). Our estimates suggest that seroadaptation reduced HIV transmissions by 98%. Potentially effective HIV prevention strategies, such as seroadaptation, have evolved in communities of MSM before they have been recognized in research or discussed in the public health forum. Thus, to be informative, studies of HIV risk must be designed to assess seroadaptive behaviors rather than be limited to individual characteristics, unprotected intercourse, and numbers of partners. STI surveillance is not an effective indicator of trends in HIV incidence where there are strong patterns of seroadaptation.

Analysis of GABAergic and Non-GABAergic Neuron Activity in the Optic Lobes of the Forager and Re-Orienting Worker Honeybee (Apis mellifera L.):

European honeybee (Apis mellifera L.) foragers have a highly developed visual system that is used for navigation. To clarify the neural basis underlying the highly sophisticated visual ability of foragers, we investigated the neural activity pattern of the optic lobes (OLs) in pollen-foragers and re-orienting bees, using the immediate early gene kakusei as a neural activity marker. We performed double-in situ hybridization of kakusei and Amgad, the honeybee homolog of the GABA synthesizing enzyme GAD, to assess inhibitory neural activity. kakusei-related activity in GABAergic and non-GABAergic neurons was strongly upregulated in the OLs of the foragers and re-orienting bees, suggesting that both types of neurons are involved in visual information processing. GABAergic neuron activity was significantly higher than non-GABAergic neuron activity in a part of the OLs of only the forager, suggesting that unique information processing occurs in the OLs of foragers. In contrast, GABAergic neuron activity in the antennal lobe was significantly lower than that of GABAergic neurons in the OLs in the forager and re-orienting bees, suggesting that kakusei-related visual activity is dominant in the brains of these bees. The present study provides the first evidence that GABAergic neurons are highly active in the OL neurons of free-moving honeybees and essential clue to reveal neural basis of the sophisticated visual ability that is equipped in the small and simple brain.

A Predominantly Neolithic Origin for European Paternal Lineages:

Arguably the most important cultural transition in the history of modern humans was the development of farming, since it heralded the population growth that culminated in our current massive population size. The genetic diversity of modern populations retains the traces of such past events, and can therefore be studied to illuminate the demographic processes involved in past events. Much debate has focused on the origins of agriculture in Europe some 10,000 years ago, and in particular whether its westerly spread from the Near East was driven by farmers themselves migrating, or by the transmission of ideas and technologies to indigenous hunter-gatherers. This study examines the diversity of the paternally inherited Y chromosome, focusing on the commonest lineage in Europe. The distribution of this lineage, the diversity within it, and estimates of its age all suggest that it spread with farming from the Near East. Taken with evidence on the origins of other lineages, this indicates that most European Y chromosomes descend from Near Eastern farmers. In contrast, most maternal lineages descend from hunter-gatherers, suggesting a reproductive advantage for farming males over indigenous hunter-gatherer males during the cultural transition from hunting-gathering to farming.

University of California Research Seminar Network: A Prospectus:

The infectious enthusiasm of scholars speaking about their research is often perfectly complemented by the never-ending quest of academic audiences for new knowledge, making seminars one of the most forceful and efficient mechanisms for transmitting scholarly information. Indeed, seminar attendance is an integral part of the experience for University of California (UC) researchers, with an estimated 300 to 500 seminars during a typical week of the academic year across 900 departments or programs in the UC system. This translates to well over 10,000 seminars annually that are presented in diverse formats and various frequencies–weekly department, graduate group and center seminars, monthly or quarterly talks in distinguished scholar lecture series, and annual university lectures by eminent faculty.

The Global Health System: Linking Knowledge with Action–Learning from Malaria:

Conducting basic research, translating it into the development of new health tools, and delivering products to patients in need of them are core functions of an effective global health system [1]. Yet performing these functions is a particular challenge for diseases that primarily affect the poor in low-income countries, partly because efforts to understand diseases and develop tools to combat them are often detached from efforts to deliver interventions. For malaria, the global health system has evolved over the past century to integrate better the research, development, and delivery (R&D&D) of new products to treat and control the disease. This article traces that evolution and extracts lessons applicable to the many new challenges currently facing the global health system.

Knots: Attractive Places with High Path Tortuosity in Mouse Open Field Exploration:

Exploration is a central component of human and animal behavior that has been studied in rodents for almost a century. It is presently one of the main models for studying the interface between behavior, genetics, drugs, and the brain. Until recently the exploration of an open field by rodents has been considered to be largely stochastic. Lately, this behavior is being gradually deciphered, revealing reference places called home bases, from which the animals perform roundtrips into the environment, tracing well-trodden paths whose features contribute to our understanding of navigation, locational memory, cognition-, and emotion-related behavior. Using advanced computational tools we discover so-called knots, preferred places visited sporadically by mice. Mice perform in these places twists and turns. The measurement of speed on the way in and out of knots reveals that they are attractive for the mice. Knot formation is enhanced by stress, suggesting that stress-related arousal assigns these locales with a special significance that is reinstated by subsequent visits to them. The twists and turns could provide the mouse with multiple views that turn knots into navigational landmarks as well as with rich vestibular input that might improve the perception and subsequent interpretation of the visual input.

How Synchronization Protects from Noise:

Synchronization phenomena are pervasive in biology, creating collective behavior out of local interactions between neurons, cells, or animals. On the other hand, many of these systems function in the presence of large amounts of noise or disturbances, making one wonder how meaningful behavior can arise in these highly perturbed conditions. In this paper we show mathematically, in a general context, that synchronization is actually a means to protect interconnected systems from effects of noise and disturbances. One possible mechanism for synchronization is that the systems jointly create and then share a common signal, such as a mean electrical field or a global chemical concentration, which in turn makes each system directly connected to all others. Conversely, extracting meaningful information from average measurements over populations of cells (as commonly used for instance in electro-encephalography, or more recently in brain-machine interfaces) may require the presence of synchronization mechanisms similar to those we describe.

Rising from the Ashes: DNA Repair in Deinococcus radiodurans:

The extraordinary resistance of Deinococcus radiodurans to ionizing radiation (IR) and desiccation is slowly drawing more intense scrutiny. Relative to most other organisms, Deinococcus has a survival advantage measured in orders of magnitude. Exposure to 5 kGy of IR reduces the genome of any bacterium to hundreds of fragments. Deinococcus is no exception. However, Deinococcus seems to take this catastrophe in stride. Over a period of 3-4 hours, overlapping fragments are spliced together into complete chromosomes, and the cells soon resume normal growth. There is no measurable lethality. Attempts to understand the molecular basis of this phoenix-like capability has given rise to numerous hypotheses. Notable among them are proposals that the condensed nature of the Deinococcus genome [1] or an unusual capacity to avoid protein oxidation [2] are keys to radiation resistance.

Non-Coding Changes Cause Sex-Specific Wing Size Differences between Closely Related Species of Nasonia:

The regulation of cell size and cell numbers is an important part of determining the size of organs in development, as well as of controlling cell over-proliferation in diseases such as cancer and diabetes. How the regulation of cell size and number can change to produce different organ sizes is not well understood. Here, we investigate the recent evolution of sex-specific wing size differences between two species that involve changes to cell size and number regulation. Males of the emerging genetic model wasp Nasonia vitripennis have small wings and do not fly, while males of the closely related species N. giraulti have large wings and do fly. We isolated a locus that contributes substantially to this wing size difference by increasing cell size and cell number. Surprisingly, we found that the determinant for this wing size difference is located in the non-coding region between two known transcription factors, the master sex determining gene doublesex and neurogenesis regulator prospero. The mechanism by which ws1 regulates sex specific wing growth has yet to be determined, although differences in dsx expression level in developing male wings may indicate a role for this sex determination locus.

Climate Change and Risk of Leishmaniasis in North America: Predictions from Ecological Niche Models of Vector and Reservoir Species:

We explored the consequences of climate change for the spread of leishmaniasis in North America. We modeled the distribution of two sand fly vector and four rodent reservoir species found in northern México and the southern United States. Models were based on occurrence data and environmental and topographic layers. Successful models were projected to 2020, 2050, and 2080 using an extreme (A2) and a conservative (B2) future climate scenario. We predicted potential range shifts of vector and reservoir species varying assumptions about dispersal ability and capacity to persist in habitats with different degrees of ecological suitability. Even with the most conservative assumptions the distributions of both vector and reservoir species expand northwards, potentially reaching as far as southern Canada in the east. Assuming that at least one vector and one reservoir species must be present for a parasite cycle, the extent of this shift is predicted to be controlled by the availability of suitable habitat for sand fly vector species. Finally, we computed the human population potentially exposed to leishmaniasis because of these range shifts. Even in the most optimistic scenario we found that twice as many individuals could be exposed to leishmaniasis in North America in 2080 compared to today.

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