Interplay between yawning and vigilance: a review of the experimental evidence

Yawning is a phylogenetically old behavior of ubiquitous occurrence. The origin and function of this conspicuous phenomenon have been subject to speculation for centuries. A widely held hypothesis posits that yawning increases the arousal level during sleepiness; thus, providing a homeostatic regulation of vigilance.

Experimental evidence for trait utility of gill raker number in adaptive radiation of a north temperate fish

North temperate fish in post-glacial lakes are textbook examples for rapid parallel adaptive radiation into multiple trophic specialists within individual lakes. Speciation repeatedly proceeded along the benthic – limnetic habitat axis, and benthic – limnetic sister species diverge in the number of gill rakers. Yet, the utility of different numbers of gill rakers for consuming benthic vs. limnetic food has only very rarely been experimentally demonstrated. We bred and raised families of a benthic – limnetic species pair of whitefish under common garden conditions to test whether these species (i) show heritable differentiation in feeding efficiency on zooplankton, and (ii) whether varia- tion in feeding efficiency is predicted by variation in gill raker numbers. We used zooplankton of three different size classes to investigate prey size dependency of divergence in feeding efficiency and to investigate the effect strength of variation in the number of gill rakers. Our results show strong interspecific differences in feeding efficiency. These differences are largest when fish were tested with the smallest zooplankton. Importantly, feeding efficiency is significantly positively correlated with the number of gill rakers when using small zooplankton, also when species identity is statistically controlled for. Our results support the hypothesis that a larger number of gill rakers are of adaptive significance for feeding on zooplankton and pro- vide one of the first experimental demonstrations of trait utility of gill raker number when fish feed on zooplankton. These results are consistent with the suggested importance of divergent selection driven feeding adaptation during adaptive radiation of fish in post-glacial lakes.

Experimental evidence for the immediate impact of fertilization and irrigation upon the plant and invertebrate communities of mountain grasslands

The response of montane and subalpine hay meadow plant and arthropod communities to the application of liquid manure and aerial irrigation – two novel, rapidly spreading management practices – remains poorly understood, which hampers the formulation of best practice management recommendations for both hay production and biodiversity preservation. In these nutrient-poor mountain grasslands, a moderate management regime could enhance overall conditions for biodiversity. This study experimentally assessed, at the site scale, among low-input montane and subalpine meadows, the short-term effects (1 year) of a moderate intensification (slurry fertilization: 26.7–53.3 kg N·ha−1·year−1; irrigation with sprinklers: 20 mm·week−1; singly or combined together) on plant species richness, vegetation structure, hay production, and arthropod abundance and biomass in the inner European Alps (Valais, SW Switzerland). Results show that (1) montane and subalpine hay meadow ecological communities respond very rapidly to an intensification of management practices; (2) on a short-term basis, a moderate intensification of very low-input hay meadows has positive effects on plant species richness, vegetation structure, hay production, and arthropod abundance and biomass; (3) vegetation structure is likely to be the key factor limiting arthropod abundance and biomass. Our ongoing experiments will in the longer term identify which level of management intensity achieves an optimal balance between biodiversity and hay production.

Ethical Consumption and Social Context: Experimental Evidence from Germany and the United States

This research examines the role of social context in ethical consumption, specifically, the extent to which anonymity and social control influence individuals' decisions to purchase organic and Fair Trade coffee. Our research design overcomes biases of prior research by combining framing and discrete choice experiments in a survey. We systematically vary coffee growing method (organic or not), import status (Fair Trade or not), flavor, and price across four social contexts that vary in degree of anonymity and normative social control. The social contexts are buying coffee online, in a large grocery store, in a small neighborhood shop, and for a meeting of a human rights group. Subjects comprise 1,103 German and American undergraduate students. We find that social context indeed influences subjects' ethical consumer decisions, especially in situations with low anonymity and high social control. In addition, gender, coffee buying, and subjective social norms trigger heterogeneity regarding stated ethical consumption and the effects of social context. These results suggest previous research has underestimated the relevance of social context for ethical consumption and overestimated altruistic motives of ethical consumers. Our study demonstrates the great potential of discrete choice experiments for the study of social action and decision making processes in sociology.

Experimental Evidence of an Eco-evolutionary Feedback during Adaptive Divergence

Differences in how organisms modify their environment can evolve rapidly and might influence adaptive population divergence [1, 2]. In a common garden experiment in aquatic mesocosms, we found that adult stickleback from a recently diverged pair of lake and stream populations had contrasting effects on ecosystem metrics. These modifications were caused by both genetic and plastic differences between populations and were sometimes comparable in magnitude to those caused by the presence/ absence of stickleback. Lake and streamfish differentially affected the biomass of zooplankton and phytoplankton, the concentration of phosphorus, and the abundance of several prey (e.g., copepods) and non-prey (e.g., cyanobacteria) species. The adult mediated effects on mesocosm ecosystems influenced the survival and growth of a subsequent generation of juvenile stickleback reared in the same mesocosms. The prior presence of adults decreased the overall growth rate of juveniles, and the prior presence of stream adults lowered overall juvenile survival. Among the survivors, lake juveniles grew faster than co-occurring stream juveniles, except in mesocosm ecosystems previously modified by adult lake fish that were reared on plankton. Overall, our results provide evidence for reciprocal interactions between ecosystem dynamics and evolutionary change (i.e., eco-evolutionary feedbacks) in the early stages of adaptive population divergence.

Body Mass Index and Cancer Risk: The Evidence for Causal Association

Increased body mass index (BMI), as an approximation of body adiposity, is a risk factor for developing several adult malignancies. To quantify these risks, we reported a comprehensive systematic review (Lancet 2008; 371: 569-78) of prospective observational studies determining associations between BMI and risk of incident cancer for 20 cancer types. We demonstrated that associations are: (i) sex-specific; (ii) exist for a wider range of malignancies than previously thought; and (iii) are broadly consistent across geographic populations. In the present paper, we tested these data against the Bradford-Hill criteria of causal association, and argue that the available data support strength of association, consistency, specificity, temporality, biological gradient, plausibility, coherence and probably analogy. However, the experimental evidence supporting reversibility is currently lacking, though indirect evidence from longitudinal data in cohort studies and long-term follow-up post-bariatric surgery is emerging. We additionally assessed these data against appropriate adjustment for available confounding factors; measurement error and study design; and residual confounding; and found lack of alternative explanations. We conclude that there is considerable evidence to support a causal association between BMI and risk for many cancer types, but in order to establish the role of weight control in cancer prevention, there is a need to develop trial frameworks in which to better test reversibility.

Drug antigenicity, immunogenicity, and costimulatory signaling: evidence for formation of a functional antigen through immune cell metabolism

Recognition of drugs by immune cells is usually explained by the hapten model, which states that endogenous metabolites bind irreversibly to protein to stimulate immune cells. Synthetic metabolites interact directly with protein-generating antigenic determinants for T cells; however, experimental evidence relating intracellular metabolism in immune cells and the generation of physiologically relevant Ags to functional immune responses is lacking. The aim of this study was to develop an integrated approach using animal and human experimental systems to characterize sulfamethoxazole (SMX) metabolism-derived antigenic protein adduct formation in immune cells and define the relationship among adduct formation, cell death, costimulatory signaling, and stimulation of a T cell response. Formation of SMX-derived adducts in APCs was dose and time dependent, detectable at nontoxic concentrations, and dependent on drug-metabolizing enzyme activity. Adduct formation above a threshold induced necrotic cell death, dendritic cell costimulatory molecule expression, and cytokine secretion. APCs cultured with SMX for 16 h, the time needed for drug metabolism, stimulated T cells from sensitized mice and lymphocytes and T cell clones from allergic patients. Enzyme inhibition decreased SMX-derived protein adduct formation and the T cell response. Dendritic cells cultured with SMX and adoptively transferred to recipient mice initiated an immune response; however, T cells were stimulated with adducts derived from SMX metabolism in APCs, not the parent drug. This study shows that APCs metabolize SMX; subsequent protein binding generates a functional T cell Ag. Adduct formation above a threshold stimulates cell death, which provides a maturation signal for dendritic cells.

Why do we yawn? The importance of evidence for specific yawn-induced effects

Gallup (this issue) believes that our recent review on the function of yawning (Guggisberg et al., 2010) is unbalanced and that it ignores evidence for his thermoregulation hypothesis. Here we address these criticisms and show them to be untenable. While we never claimed that the social hypothesis of yawning has "definite experimental support", we emphasize the importance of experimental evidence for specific effects of yawns when considering why we yawn. The only specific effect of yawning that could be demonstrated so far is its contagiousness in humans, some non-human primates, and possibly dogs, whereas all studies investigating physiological consequences of yawns were unable to observe specific yawn-induced effects in the individual of any species. The argument that from an evolutionary perspective, yawns must have a "primitive" physiological function arises from imprecise reasoning.

Evidence of Adaptive Evolutionary Divergence during Biological Invasion

Rapid phenotypic diversification during biological invasions can either arise by adaptation to alternative environments or by adaptive phenotypic plasticity. Where experimental evidence for adaptive plasticity is common, support for evolutionary diversification is rare. Here, we performed a controlled laboratory experiment using full-sib crosses between ecologically divergent threespine stickleback populations to test for a genetic basis of adaptation. Our populations are from two very different habitats, lake and stream, of a recently invaded range in Switzerland and differ in ecologically relevant morphological traits. We found that in a lake-like food treatment lake fish grow faster than stream fish, resembling the difference among wild type individuals. In contrast, in a stream-like food treatment individuals from both populations grow similarly. Our experimental data suggest that genetically determined diversification has occurred within less than 140 years after the arrival of stickleback in our studied region.

Why do we yawn?

Yawning is a phylogenetically old behaviour that can be observed in most vertebrate species from foetal stages to old age. The origin and function of this conspicuous phenomenon have been subject to speculations for centuries. Here, we review the experimental evidence for each of these hypotheses. It is found that theories ascribing a physiological role to yawning (such as the respiratory, arousal, or thermoregulation hypotheses) lack evidence. Conversely, the notion that yawning has a communicative function involved in the transmission of drowsiness, boredom, or mild psychological stress receives increasing support from research in different fields. In humans and some other mammals, yawning is part of the action repertoire of advanced empathic and social skills.

Do fungal pathogens drive density-dependent mortality in established seedlings of two dominant African rain forest trees?

Where one or a few tree species reach local high abundance, different ecological factors may variously facilitate or hinder their regeneration. Plant pathogens are thought to be one of those possible agents which drive intraspecific density-dependent mortality of tree seedlings in tropical forests. Experimental evidence for this is scarce, however. In an African rain forest at Korup, we manipulated the density of recently established seedlings (~5–8 wk old; low vs. high-density) of two dominant species of contrasting recruitment potential, and altered their exposure to pathogens using a broad-spectrum fungicide. Seedling mortality of the abundantly recruiting subcanopy tree Oubanguia alata was strongly density-dependent after 7 mo, yet fungicide-treated seedlings had slightly higher mortality than controls. By contrast, seedling mortality of the poorly recruiting large canopy-emergent tree Microberlinia bisulcata was unaffected by density or fungicide. Ectomycorrhizal colonization of M. bisulcata was not affected by density or fungicide either. For O. alata, adverse effects of fungicide on its vesicular arbuscular mycorrhizas may have offset any possible benefit of pathogen removal. We tentatively conclude that fungal pathogens are not a likely major cause of density dependence in O. alata, or of early post-establishment mortality in M. bisulcata. They do not explain the latter's currently very low recruitment rate at Korup.

Cardiac Sodium Channel Nav1.5 Mechanosensitivity is Inhibited by Ranolazine

The cardiac action potential (AP) is initiated by the depolarizing inward sodium current (I(Na)). The pore-forming subunit of the cardiac sodium channel, Na(v)1.5, is the main ion channel that conducts I(Na) in cardiac cells. Despite the large number of studies investigating Na(v)1.5, year after year, we are still learning new aspects regarding its roles in normal cardiac function and in diseased states. The clinical relevance of this channel cannot be understated. The cardiac I(Na) is the target of the class 1 anti-arrhythmic drugs(1), which are nowadays less frequently prescribed because of their well-documented pro-arrhythmic properties(2). In addition, since the first description in 1995 by Keating's group(3) of mutations in patients suffering from congenital long QT syndrome (LQTS) type 3, several hundred genetic variants in SCN5A, the gene coding for Na(v)1.5, have been reported and investigated(4). Interestingly, many of these genetic variants have been found in patients with diverse cardiac manifestations(5) such as congenital LQTS type 3, Brugada syndrome, conduction disorders, and more recently, atrial fibrillation and dilated cardiomyopathy. This impressive list underlines the importance of Na(v)1.5 in cardiac pathologies and raises the question about possible unknown roles and regulatory mechanisms of this channel in cardiac cells. Recent studies have provided experimental evidence that the function of Na(v)1.5, among many other described regulatory mechanisms(6), is also modulated by the mechanical stretch of the membrane in which it is embedded(7), thus suggesting that Na(v)1.5, like other ion channels, is "mechanosensitive". What does this mean? (SELECT FULL TEXT TO CONTINUE).

Hit proteins, mitochondria and cancer

The histidine triad (HIT) superfamily comprises proteins that share the histidine triad motif, His-ϕ-His-ϕ-His-ϕ-ϕ, where ϕ is a hydrophobic amino acid. HIT proteins are ubiquitous in prokaryotes and eukaryotes. HIT proteins bind nucleotides and exert dinucleotidyl hydrolase, nucleotidylyl transferase or phosphoramidate hydrolase enzymatic activity. In humans, 5 families of HIT proteins are recognized. The accumulated epidemiological and experimental evidence indicates that two branches of the superfamily, the HINT (Histidine Triad Nucleotide Binding) members and FHIT (Fragile Histidine Triad), have tumor suppressor properties but a conclusive physiological role can still not be assigned to these proteins. Aprataxin forms another discrete branch of the HIT superfamily, is implicated in DNA repair mechanisms and unlike the HINT and FHIT members, a defective protein can be conclusively linked to a disease, ataxia with oculomotor apraxia type 1. The scavenger mRNA decapping enzyme, DcpS, forms a fourth branch of the HIT superfamily. Finally, the GalT enzymes, which exert specific nucleoside monophosphate transferase activity, form a fifth branch that is not implicated in tumorigenesis. The molecular mechanisms by which the HINT and FHIT proteins participate in bioenergetics of cancer are just beginning to be unraveled. Their purported actions as tumor suppressors are highlighted in this review.