Sorry for missing in action. Lots of new articles in various PLoS journals yesterday and 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, Mendeley, 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:
Distinguishing between a fair and unfair tackle in soccer can be difficult. For referees, choosing to call a foul often requires a decision despite some level of ambiguity. We were interested in whether a well documented perceptual-motor bias associated with reading direction influenced foul judgments. Prior studies have shown that readers of left-to-right languages tend to think of prototypical events as unfolding concordantly, from left-to-right in space. It follows that events moving from right-to-left should be perceived as atypical and relatively debased. In an experiment using a go/no-go task and photographs taken from real games, participants made more foul calls for pictures depicting left-moving events compared to pictures depicting right-moving events. These data suggest that two referees watching the same play from distinct vantage points may be differentially predisposed to call a foul.
Normally, in sexually reproducing organisms, the sex ratio (ratio of males to females) is 1:1. However, examples are known where this is not the case and there are more females than males in a population. Extreme bias in sex ratio can lead to females failing to find a mate. We studied Cheilomenes sexmaculata, a ladybird species that has females that produce more female than male offspring. In aphid-eating ladybirds, this phenomenon has been widely reported and is known to be due to the presence of bacteria that live inside the mother and are passed via her eggs to her offspring. In eggs destined to become male, the bacteria kill the embryo by some unknown mechanism. This is known as male-killing. Female offspring develop normally. Evolutionary theory predicts that in such systems, the genome of the host can fight back if a variant arises that stops the bacteria killing male offspring. In C. sexmaculata we found females that carried the male-killer but the sex ratio of their offspring depended on the male that they mated with. We carried out breeding tests to show that some ladybirds had a version of a gene that rescued the male offspring from the pathological effects of the male-killer.
Differential herbivory and/or differential plant resistance or tolerance in sun and shade environments may influence plant distribution along the light gradient. Embothrium coccineum is one of the few light-demanding tree species in the temperate rainforest of southern South America, and seedlings are frequently attacked by insects and snails. Herbivory may contribute to the exclusion of E. coccineum from the shade if 1) herbivory pressure is greater in the shade, which in turn can result from shade plants being less resistant or from habitat preferences of herbivores, and/or 2) consequences of damage are more detrimental in the shade, i.e., shade plants are less tolerant. We tested this in a field study with naturally established seedlings in treefall gaps (sun) and forest understory (shade) in a temperate rainforest of southern Chile. Seedlings growing in the sun sustained nearly 40% more herbivore damage and displayed half of the specific leaf area than those growing in the shade. A palatability test showed that a generalist snail consumed ten times more leaf area when fed on shade leaves compared to sun leaves, i.e., plant resistance was greater in sun-grown seedlings. Herbivore abundance (total biomass) was two-fold greater in treefall gaps compared to the forest understory. Undamaged seedlings survived better and showed a slightly higher growth rate in the sun. Whereas simulated herbivory in the shade decreased seedling survival and growth by 34% and 19%, respectively, damaged and undamaged seedlings showed similar survival and growth in the sun. Leaf tissue lost to herbivores in the shade appears to be too expensive to replace under the limiting light conditions of forest understory. Following evaluations of herbivore abundance and plant resistance and tolerance in contrasting light environments, we have shown how herbivory on a light-demanding tree species may contribute to its exclusion from shade sites. Thus, in the shaded forest understory, where the seedlings of some tree species are close to their physiological tolerance limit, herbivory could play an important role in plant establishment.
Traditional treatment of bacterial infections relies heavily on the use of antibacterial compounds that either kill bacteria (bactericidal) or inhibit their growth (bacteriostatic). Typically, the targets for the main conventional antibiotics are essential cellular processes such as bacterial cell wall biosynthesis, bacterial protein synthesis, and bacterial DNA replication and repair. However, resistance to these drugs arises and spreads very rapidly, even to such an extent that bacteria have been identified that are simultaneously resistant to all available antibiotics . The increasing occurrence of resistant bacteria gradually renders antibiotics ineffective in treating infections and has enormous human and economic consequences worldwide. As a result, the identification of novel drug targets and the development of novel therapeutics constitute an important area of current scientific research. An alternative to killing or inhibiting growth of pathogenic bacteria is the specific attenuation of bacterial virulence, which can be attained by targeting key regulatory systems that mediate the expression of virulence factors. One of the target regulatory systems is quorum sensing (QS), or bacterial cell-to-cell communication. QS is a mechanism of gene regulation in which bacteria coordinate the expression of certain genes in response to the presence or absence of small signal molecules (Figure 1).
Can hearing a word change what one sees? Although visual sensitivity is known to be enhanced by attending to the location of the target, perceptual enhancements of following cues to the identity of an object have been difficult to find. Here, we show that perceptual sensitivity is enhanced by verbal, but not visual cues. Participants completed an object detection task in which they made an object-presence or -absence decision to briefly-presented letters. Hearing the letter name prior to the detection task increased perceptual sensitivity (dâ²). A visual cue in the form of a preview of the to-be-detected letter did not. Follow-up experiments found that the auditory cuing effect was specific to validly cued stimuli. The magnitude of the cuing effect positively correlated with an individual measure of vividness of mental imagery; introducing uncertainty into the position of the stimulus did not reduce the magnitude of the cuing effect, but eliminated the correlation with mental imagery. Hearing a word made otherwise invisible objects visible. Interestingly, seeing a preview of the target stimulus did not similarly enhance detection of the target. These results are compatible with an account in which auditory verbal labels modulate lower-level visual processing. The findings show that a verbal cue in the form of hearing a word can influence even the most elementary visual processing and inform our understanding of how language affects perception.
Adaptation of sessile animals, such as molluscs, to stress is achieved by a number of molecular mechanisms, few of which are clearly understood. Insights from this research can provide clues about stress tolerance both for sessile and mobile organisms. The Mediterranean mussel, of the genus Mytilus, is a model organism for the study of stress at the molecular level, with sufficient gene structure and function data available. We have thus investigated a key stress response gene, Hsp90, and in particular its upstream region, using a combination of sequence and expression analysis approaches. We demonstrate that this region, responsible for the regulation of heat shock-associated gene expression, exhibits an unparalleled structural and functional complexity compared to other model organisms, as well as subtle gene expression patterns across multiple tissues. These results form the basis upon which the heat shock response can be used as a molecular biosensor for environmental monitoring in the future.
Anecdotal information and case reports suggest that intravenously administered vitamin C is used by Complementary and Alternate Medicine (CAM) practitioners. The scale of such use in the U.S. and associated side effects are unknown. We surveyed attendees at annual CAM Conferences in 2006 and 2008, and determined sales of intravenous vitamin C by major U.S. manufacturers/distributors. We also queried practitioners for side effects, compiled published cases, and analyzed FDA's Adverse Events Database. Of 199 survey respondents (out of 550), 172 practitioners administered IV vitamin C to 11,233 patients in 2006 and 8876 patients in 2008. Average dose was 28 grams every 4 days, with 22 total treatments per patient. Estimated yearly doses used (as 25g/50ml vials) were 318,539 in 2006 and 354,647 in 2008. Manufacturers' yearly sales were 750,000 and 855,000 vials, respectively. Common reasons for treatment included infection, cancer, and fatigue. Of 9,328 patients for whom data is available, 101 had side effects, mostly minor, including lethargy/fatigue in 59 patients, change in mental status in 21 patients and vein irritation/phlebitis in 6 patients. Publications documented serious adverse events, including 2 deaths in patients known to be at risk for IV vitamin C. Due to confounding causes, the FDA Adverse Events Database was uninformative. Total numbers of patients treated in the US with high dose vitamin C cannot be accurately estimated from this study. High dose IV vitamin C is in unexpectedly wide use by CAM practitioners. Other than the known complications of IV vitamin C in those with renal impairment or glucose 6 phosphate dehydrogenase deficiency, high dose intravenous vitamin C appears to be remarkably safe. Physicians should inquire about IV vitamin C use in patients with cancer, chronic, untreatable, or intractable conditions and be observant of unexpected harm, drug interactions, or benefit.
Neurons communicate primarily with stereotypical electrical impulses, action potentials, which are fired when a threshold level of excitation is reached. This threshold varies between cells and over time as a function of previous stimulations, which has major functional implications on the integrative properties of neurons. Ionic channels are thought to play a central role in this modulation but the precise relationship between their properties and the threshold is unclear. We examined this relationship in biophysical models and derived a formula which quantifies the contribution of various mechanisms. The originality of our approach is that it provides an instantaneous time-varying value for the threshold, which applies to the highly fluctuating regimes characterizing neurons in vivo. In particular, two known ionic mechanisms were found to make the threshold adapt to the membrane potential, thus providing the cell with a form of gain control.
Uncertainty and predictability have remained at the center of the study of human attention. Yet, studies have only examined whether response times (RT) or fixations were longer or shorter under levels of stimulus uncertainty. To date, no study has examined patterns of stimuli and responses through a unifying framework of uncertainty. We asked 29 college students to generate repeated responses to a continuous series of visual stimuli presented on a computer monitor. Subjects produced these responses by pressing on a keypad as soon a target was detected (regardless of position) while the durations of their visual fixations were recorded. We manipulated the level of stimulus uncertainty in space and time by changing the number of potential stimulus locations and time intervals between stimulus presentations. To allow the analyses to be conducted using uncertainty as common description of stimulus and response we calculated the entropy of the RT and fixation durations. We tested the hypothesis of uncertainty compensation across space and time by fitting the RT and fixation duration entropy values to a quadratic surface. The quadratic surface accounted for 80% of the variance in the entropy values of both RT and fixation durations. RT entropy increased as a function of spatial and temporal uncertainty of the stimulus, alongside a symmetric, compensatory decrease in the entropy of fixation durations as the level of spatial and temporal uncertainty of the stimuli was increased. Our results demonstrate that greater uncertainty in the stimulus leads to greater uncertainty in the response, and that the effects of spatial and temporal uncertainties are compensatory. We also observed compensatory relationship across the entropies of fixation duration and RT, suggesting that a more predictable visual search strategy leads to more uncertain response patterns and vice versa.
Classical morphological taxonomy places the approximately 1400 recognized species of Scleractinia (hard corals) into 27 families, but many aspects of coral evolution remain unclear despite the application of molecular phylogenetic methods. In part, this may be a consequence of such studies focusing on the reef-building (shallow water and zooxanthellate) Scleractinia, and largely ignoring the large number of deep-sea species. To better understand broad patterns of coral evolution, we generated molecular data for a broad and representative range of deep sea scleractinians collected off New Caledonia and Australia during the last decade, and conducted the most comprehensive molecular phylogenetic analysis to date of the order Scleractinia. Partial (595 bp) sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene were determined for 65 deep-sea (azooxanthellate) scleractinians and 11 shallow-water species. These new data were aligned with 158 published sequences, generating a 234 taxon dataset representing 25 of the 27 currently recognized scleractinian families. There was a striking discrepancy between the taxonomic validity of coral families consisting predominantly of deep-sea or shallow-water species. Most families composed predominantly of deep-sea azooxanthellate species were monophyletic in both maximum likelihood and Bayesian analyses but, by contrast (and consistent with previous studies), most families composed predominantly of shallow-water zooxanthellate taxa were polyphyletic, although Acroporidae, Poritidae, Pocilloporidae, and Fungiidae were exceptions to this general pattern. One factor contributing to this inconsistency may be the greater environmental stability of deep-sea environments, effectively removing taxonomic "noise" contributed by phenotypic plasticity. Our phylogenetic analyses imply that the most basal extant scleractinians are azooxanthellate solitary corals from deep-water, their divergence predating that of the robust and complex corals. Deep-sea corals are likely to be critical to understanding anthozoan evolution and the origins of the Scleractinia.