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So, let’s see what’s new in PLoS Genetics, PLoS Computational Biology, PLoS Pathogens and PLoS ONE this week. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. Here are my own picks for the week – you go and look for your own favourites:
Developmental Constraints on Vertebrate Genome Evolution:

Because embryonic development must proceed correctly for an animal to survive, changes in evolution are constrained according to their effects on development. Changes that disrupt development too dramatically are thus rare in evolution. While this has been long observed at the morphological level, it has been more difficult to characterize the impact of such constraints on the genome. In this study, we investigate the effect of gene expression over vertebrate developmental time (from early to late development) on two main features: the gravity of mutation effects (i.e., is removal of the gene lethal?) and the propensity of the gene to remain in double copy after a duplication. We see that both features are consistent, in both zebrafish and mouse, in indicating a strong effect of constraints, which are progressively weaker towards late development, in early development on the genome.

Sexually Antagonistic “Zygotic Drive” of the Sex Chromosomes:

Our study describes a new form of sexual genomic conflict that operates through the process of antagonistic green-beard effects. Although past theoretical and empirical work indicated that green-beard effects rarely operate in nature, our new theory shows why this conclusion may have to be reevaluated. We integrate modeling analysis with extant empirical work to show that the unique properties of sex chromosomes can lead to a previously unappreciated form of sexual conflict (sexually antagonistic zygotic drive) that may be widespread in nature. It operates through harmful epigenetic parental effects, asymmetrical allocation of parental investment to sons and daughters, and asymmetrical interactions between brothers and sisters. Sexually antagonistic zygotic drive is functionally analogous to meiotic drive except that it operates due to competition among opposite-sex siblings rather than between competing gametes.

Frequent Toggling between Alternative Amino Acids Is Driven by Selection in HIV-1:

Viruses, such as HIV, are able to evade host immune responses through escape mutations, yet sometimes they do so at a cost. This cost is the reduction in the ability of the virus to replicate, and thus selective pressure exists for a virus to revert to its original state in the absence of the host immune response that caused the initial escape mutation. This pattern of escape and reversion typically occurs when viruses are transmitted between individuals with different immune responses. We develop a phylogenetic model of immune escape and reversion and provide evidence that it outperforms existing models for the detection of selective pressure associated with host immune responses. Finally, we demonstrate that amino acid toggling is a pervasive process in HIV-1 evolution, such that many of the positions in the virus that evolve rapidly, under the influence of positive Darwinian selection, nonetheless display quite low sequence diversity. This highlights the limitations of HIV-1 evolution, and sites such as these are potentially good targets for HIV-1 vaccines.

Never Resting Brain: Simultaneous Representation of Two Alpha Related Processes in Humans:

Brain activity is continuously modulated, even at “rest”. The alpha rhythm (8-12 Hz) has been known as the hallmark of the brain’s idle-state. However, it is still debated if the alpha rhythm reflects synchronization in a distributed network or focal generator and whether it occurs spontaneously or is driven by a stimulus. This EEG/fMRI study aimed to explore the source of alpha modulations and their distribution in the resting brain. By serendipity, while computing the individually defined power modulations of the alpha-band, two simultaneously occurring components of these modulations were found. An ‘induced alpha’ that was correlated with the paradigm (eyes open/ eyes closed), and a ‘spontaneous alpha’ that was on-going and unrelated to the paradigm. These alpha components when used as regressors for BOLD activation revealed two segregated activation maps: the ‘induced map’ included left lateral temporal cortical regions and the hippocampus; the ‘spontaneous map’ included prefrontal cortical regions and the thalamus. Our combined fMRI/EEG approach allowed to computationally untangle two parallel patterns of alpha modulations and underpin their anatomical basis in the human brain. These findings suggest that the human alpha rhythm represents at least two simultaneously occurring processes which characterize the ‘resting brain’; one is related to expected change in sensory information, while the other is endogenous and independent of stimulus change.

Interpersonal Trust and Quality-of-Life: A Cross-Sectional Study in Japan:

There is growing interest in psychosocial factors with positive attitudes, such as interpersonal trust, as determinants for Quality-of-life (QOL) or subjective well-being. Despite their longevity, Japanese people report a relatively poor subjective well-being, as well as lower interpersonal trust. Our aim in this study was to evaluate the possible association between interpersonal trust and QOL among Japanese people. Based on the cross-sectional data for Japanese adults (2008), we analyzed the relationship between interpersonal trust and each of four domains of the WHOQOL-BREF. Interpersonal trust was assessed using three scales for trust in people, in human fairness and in human nature. In a total of 1000 participants (mean age: 45 years; 49% women), greater trust was recognized among women (vs. men), those aged 60-69 (vs. 20-29), or the high-income group (vs. low-income). Each of three trust scales was positively correlated with all domains of QOL. Multiple linear-regression models were constructed for each of QOL and the principal component score of the trust scales, adjusted for age, gender, area size of residence, income, education, and occupation. For all QOL domains, interpersonal trust was significantly and positively associated with better QOL with p<0.001 for all four domains including physical, psychological, social, and environmental QOL. Other factors associated with QOL included gender, age class, area size of residence, and income. Education and occupation were not associated with QOL. Greater interpersonal trust is strongly associated with a better QOL among Japanese adults. If a causal relationship is demonstrated in a controlled interventional study, social and political measures should be advocated to increase interpersonal trust for achieving better QOL.

Starting High School One Hour Later May Reduce Teen Traffic Accidents:

A new study shows that after a one-hour delay of school start times, teens increased their average nightly hours of sleep and decreased their “catch-up sleep” on the weekends, and they were involved in fewer auto accidents.

Low Dose Of Caffeine When Pregnant May Damage Heart Of Offspring For A Lifetime:

A new study shows that the equivalent of one dose of caffeine (just two cups of coffee) ingested during pregnancy may be enough to affect fetal heart development and then reduce heart function over the entire lifespan of the child. In addition, the researchers also found that this relatively minimal amount of exposure may lead to higher body fat among males, when compared to those who were not exposed to caffeine.

Tiny Magnetic Crystals In Bacteria Are A Compass, Say Scientists:

Scientists have shown that tiny crystals found inside bacteria provide a magnetic compass to help them navigate through sediment to find the best food. Researchers say their study could provide fresh clues to explain biomagnetism – a phenomenon in which some birds, insects and marine life navigate using the magnetic field that encompasses the Earth.

Global Warming Impacts On U.S. Coming Sooner Than Expected, Report Predicts:

A report released at the annual meeting of the American Geophysical Union on December 16 provides new insights on the potential for abrupt climate change and the effects it could have on the United States, identifying key concerns that include faster-than-expected loss of sea ice, rising sea levels and a possibly permanent state of drought in the American Southwest.

Hmmm so it seems that we have to abandon some old cherished beliefs:
Scientists debunk the myth that you lose most heat through your head:

When it comes to wrapping up on a cold winter’s day, a cosy hat is obligatory. After all, most of our body heat is lost through our heads – or so we are led to believe.
Closer inspection of heat loss in the hatless, however, reveals the claim to be nonsense, say scientists who have dispelled this and five other modern myths.
They traced the origins of the hat-wearing advice back to a US army survival manual from 1970 which strongly recommended covering the head when it is cold, since “40 to 45 percent of body heat” is lost from the head.
Rachel Vreeman and Aaron Carroll, at the centre for health policy at Indiana University in Indianapolis, rubbish the claim in the British Medical Journal this week. If this were true, they say, humans would be just as cold if they went without a hat as if they went without trousers. “Patently, this is just not the case,” they write.
The myth is thought to have arisen through a flawed interpretation of a vaguely scientific experiment by the US military in the 1950s. In those studies, volunteers were dressed in Arctic survival suits and exposed to bitterly cold conditions. Because it was the only part of their bodies left uncovered, most of their heat was lost through their heads.
The face, head and chest are more sensitive to changes in temperature than the rest of the body, making it feel as if covering them up does more to prevent heat loss. In fact, covering one part of the body has as much effect as covering any other. If the experiment had been performed with people wearing only swimming trunks, they would have lost no more than 10% of their body heat through their heads, the scientists add.

Why Do We Yawn?:

Even though yawning is very common, the physiological and evolutionary reasons for yawning behavior are poorly understood.
Yawning is a familiar behavior characterized by a large gaping of the mouth, accompanied by a deep inhalation of air, followed a shorter expiration. This behavior is under involuntary control, so it cannot be consciously controlled or suppressed. Further, yawning is a stereotyped behavior expressed by all classes of animals, and is correlated by a variety of neurochemical changes in the brain. Previous research suggests that yawning is a biological mechanism in humans and non-human apes, such as chimpanzees, to keep the brain from overheating.
“Brains are like computers,” reports Andrew Gallup, a researcher in the Department of Biology at Binghamton University who led the study. “They operate most efficiently when cool, and physical adaptations have evolved to allow maximum cooling of the brain.”
This is known as the “radiator hypothesis” or the “brain-cooling hypothesis,” which can be tested.
“Based on the brain-cooling hypothesis, we suggest that there should be a thermal window in which yawning should occur,” Gallup proposed. “For instance, yawning should not occur when ambient temperatures exceed body temperature, as taking a deep inhalation of warm air would be counterproductive. In addition, yawning when it is extremely cold may be maladaptive, as this may send unusually cold air to the brain, which may produce a thermal shock.”
To test this hypothesis, Gallup and his colleagues, Michael Miller and Anne Clark, studied yawning in wild budgerigars, Melopsittacus undulatus. They chose budgerigars because they have relatively large brains for their body size, they live wild in arid regions of Australia that are subject to frequent and dramatic temperature changes, and — most important for their experimental design, where they tested the birds in small groups — budgerigars do not experience contagious or sympathetic yawning, as humans and some other animals do….

There are 13 new articles in PLoS ONE today. 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, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
Perinatal Caffeine, Acting on Maternal Adenosine A1 Receptors, Causes Long-Lasting Behavioral Changes in Mouse Offspring:

There are lingering concerns about caffeine consumption during pregnancy or the early postnatal period, partly because there may be long-lasting behavioral changes after caffeine exposure early in life. We show that pregnant wild type (WT) mice given modest doses of caffeine (0.3 g/l in drinking water) gave birth to offspring that as adults exhibited increased locomotor activity in an open field. The offspring also responded to cocaine challenge with greater locomotor activity than mice not perinatally exposed to caffeine. We performed the same behavioral experiments on mice heterozygous for adenosine A1 receptor gene (A1RHz). In these mice signaling via adenosine A1 receptors is reduced to about the same degree as after modest consumption of caffeine. A1RHz mice had a behavioral profile similar to WT mice perinatally exposed to caffeine. Furthermore, it appeared that the mother’s genotype, not offspring’s, was critical for behavioral changes in adult offspring. Thus, if the mother partially lacked A1 receptors the offspring displayed more hyperactivity and responded more strongly to cocaine stimulation as adults than did mice of a WT mother, regardless of their genotype. This indicates that long-term behavioral alterations in the offspring result from the maternal effect of caffeine, and not a direct effect on fetus. WT offspring from WT mother but having a A1R Hz grandmother preserved higher locomotor response to cocaine. We suggest that perinatal caffeine, by acting on adenosine A1 receptors in the mother, causes long-lasting behavioral changes in the offspring that even manifest themselves in the second generation.

Ecological Thresholds in the Savanna Landscape: Developing a Protocol for Monitoring the Change in Composition and Utilisation of Large Trees:

Acquiring greater understanding of the factors causing changes in vegetation structure – particularly with the potential to cause regime shifts – is important in adaptively managed conservation areas. Large trees (≥5 m in height) play an important ecosystem function, and are associated with a stable ecological state in the African savanna. There is concern that large tree densities are declining in a number of protected areas, including the Kruger National Park, South Africa. In this paper the results of a field study designed to monitor change in a savanna system are presented and discussed. Developing the first phase of a monitoring protocol to measure the change in tree species composition, density and size distribution, whilst also identifying factors driving change. A central issue is the discrete spatial distribution of large trees in the landscape, making point sampling approaches relatively ineffective. Accordingly, fourteen 10 m wide transects were aligned perpendicular to large rivers (3.0-6.6 km in length) and eight transects were located at fixed-point photographic locations (1.0-1.6 km in length). Using accumulation curves, we established that the majority of tree species were sampled within 3 km. Furthermore, the key ecological drivers (e.g. fire, herbivory, drought and disease) which influence large tree use and impact were also recorded within 3 km. The technique presented provides an effective method for monitoring changes in large tree abundance, size distribution and use by the main ecological drivers across the savanna landscape. However, the monitoring of rare tree species would require individual marking approaches due to their low densities and specific habitat requirements. Repeat sampling intervals would vary depending on the factor of concern and proposed management mitigation. Once a monitoring protocol has been identified and evaluated, the next stage is to integrate that protocol into a decision-making system, which highlights potential leading indicators of change. Frequent monitoring would be required to establish the rate and direction of change. This approach may be useful in generating monitoring protocols for other dynamic systems.

Rapid Perceptual Switching of a Reversible Biological Figure:

Certain visual stimuli can give rise to contradictory perceptions. In this paper we examine the temporal dynamics of perceptual reversals experienced with biological motion, comparing these dynamics to those observed with other ambiguous structure from motion (SFM) stimuli. In our first experiment, naïve observers monitored perceptual alternations with an ambiguous rotating walker, a figure that randomly alternates between walking in clockwise (CW) and counter-clockwise (CCW) directions. While the number of reported reversals varied between observers, the observed dynamics (distribution of dominance durations, CW/CCW proportions) were comparable to those experienced with an ambiguous kinetic depth cylinder. In a second experiment, we compared reversal profiles with rotating and standard point-light walkers (i.e. non-rotating). Over multiple test repetitions, three out of four observers experienced consistently shorter mean percept durations with the rotating walker, suggesting that the added rotational component may speed up reversal rates with biomotion. For both stimuli, the drift in alternation rate across trial and across repetition was minimal. In our final experiment, we investigated whether reversals with the rotating walker and a non-biological object with similar global dimensions (rotating cuboid) occur at random phases of the rotation cycle. We found evidence that some observers experience peaks in the distribution of response locations that are relatively stable across sessions. Using control data, we discuss the role of eye movements in the development of these reversal patterns, and the related role of exogenous stimulus characteristics. In summary, we have demonstrated that the temporal dynamics of reversal with biological motion are similar to other forms of ambiguous SFM. We conclude that perceptual switching with biological motion is a robust bistable phenomenon.

UP States Protect Ongoing Cortical Activity from Thalamic Inputs:

Cortical neurons in vitro and in vivo fluctuate spontaneously between two stable membrane potentials: a depolarized UP state and a hyperpolarized DOWN state. UP states temporally correspond with multineuronal firing sequences which may be important for information processing. To examine how thalamic inputs interact with ongoing cortical UP state activity, we used calcium imaging and targeted whole-cell recordings of activated neurons in thalamocortical slices of mouse somatosensory cortex. Whereas thalamic stimulation during DOWN states generated multineuronal, synchronized UP states, identical stimulation during UP states had no effect on the subthreshold membrane dynamics of the vast majority of cells or on ongoing multineuronal temporal patterns. Both thalamocortical and corticocortical PSPs were significantly reduced and neuronal input resistance was significantly decreased during cortical UP states – mechanistically consistent with UP state insensitivity. Our results demonstrate that cortical dynamics during UP states are insensitive to thalamic inputs.

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There are 12 new articles in PLoS ONE today. 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, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
An Examination of Morphometric Variations in a Neotropical Toad Population (Proceratophrys cristiceps, Amphibia, Anura, Cycloramphidae):

The species Proceratophrys cristiceps belongs to the genus Proceratophrys within the family Cycloramphidae. These amphibians are found exclusively in South America in the morphoclimatic domain of the semi-arid depression zones in northeastern Brazil known as the Caatinga. We examined intrapopulational variation using univariate and multivariate statistics with traditional and geometric morphometrics, which supported the existence of two morphotypes of this species. Our results indicated significant degrees of variation in skeletal characteristics between some natural populations of this species. Careful analyses of variability levels are fundamental to avoid taxonomic errors, principally in populations that demonstrate characteristics intimately associated with their area of occurrence, as is the case of Proceratophrys cristiceps.

Size Variation in Small-Bodied Humans from Palau, Micronesia:

Recent discoveries on Palau are claimed to represent the remains of small-bodied humans that may display evidence insular size reduction. This claim has yet to be statistically validated. Published postcranial specimens (n = 16) from Palau were assessed relative to recent small-bodied comparative samples. Resampling statistical approaches were employed to test specific hypotheses relating to body size in the Palau sample. Results confirm that the Palau postcranial sample is indisputably small-bodied. A single, homogenous body size morph is represented in early prehistoric postcrania from Palau. Small body size in early Palauans is an ancestral characteristic and was likely not a consequence of in-situ size reduction. Specimens from Palau have little bearing upon hypothesised insular size reduction in the ancestral lineage of Homo floresiensis.

This is the third paper in a series, discussing this controversial find. The first two papers are:
Small-Bodied Humans from Palau, Micronesia
and
Small Scattered Fragments Do Not a Dwarf Make: Biological and Archaeological Data Indicate that Prehistoric Inhabitants of Palau Were Normal Sized

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There are a bunch of cool new articles in PLoS Medicine, PLoS Biology and PLoS Neglected Tropical Diseases today. Take a look:

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