Four out of seven PLoS journals published new articles last night - here are the ones that caught my eye. 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:
Do Decapod Crustaceans Have Nociceptors for Extreme pH?:
Nociception is the physiological detection of noxious stimuli. Because of its obvious importance, nociception is expected to be widespread across animal taxa and to trigger robust behaviours reliably. Nociception in invertebrates, such as crustaceans, is poorly studied. Three decapod crustacean species were tested for nociceptive behaviour: Louisiana red swamp crayfish (Procambarus clarkii), white shrimp (Litopenaeus setiferus), and grass shrimp (Palaemonetes sp.). Applying sodium hydroxide, hydrochloric acid, or benzocaine to the antennae caused no change in behaviour in the three species compared to controls. Animals did not groom the stimulated antenna, and there was no difference in movement of treated individuals and controls. Extracellular recordings of antennal nerves in P. clarkii revealed continual spontaneous activity, but no neurons that were reliably excited by the application of concentrated sodium hydroxide or hydrochloric acid. Previously reported responses to extreme pH are either not consistently evoked across species or were mischaracterized as nociception. There was no behavioural or physiological evidence that the antennae contained specialized nociceptors that responded to pH.
Zen Faulkes has more background information about it.
Adaptive divergence between populations in the face of strong selection on key traits can lead to morphological divergence between populations without concomitant divergence in neutral DNA. Thus, the practice of identifying genetically distinct populations based on divergence in neutral DNA may lead to a taxonomy that ignores evolutionarily important, rapidly evolving, locally-adapted populations. Providing evidence for a genetic basis of morphological divergence between rapidly evolving populations that lack divergence in selectively neutral DNA will not only inform conservation efforts but also provide insight into the mechanisms of the early processes of speciation. The coastal plain swamp sparrow, a recent colonist of tidal marsh habitat, differs from conspecific populations in a variety of phenotypic traits yet remains undifferentiated in neutral DNA. Here we use an experimental approach to demonstrate that phenotypic divergence between ecologically separated populations of swamp sparrows is the result of local adaptation despite the lack of divergence in neutral DNA. We find that morphological (bill size and plumage coloration) and life history (reproductive effort) differences observed between wild populations were maintained in laboratory raised individuals suggesting genetic divergence of fitness related traits. Our results support the hypothesis that phenotypic divergence in swamps sparrows is the result of genetic differentiation, and demonstrate that adaptive traits have evolved more rapidly than neutral DNA in these ecologically divergent populations that may be in the early stages of speciation. Thus, identifying evolutionarily important populations based on divergence in selectively neutral DNA could miss an important level of biodiversity and mislead conservation efforts.
Carbon Dioxide Sensing Modulates Lifespan and Physiology in Drosophila:
Sensory inputs, including taste and smell, can modulate lifespan in organisms such as fruit flies and nematodes. For example, the smell of live yeast is sufficient to accelerate aging in fruit flies that are nutrient restricted. However, the sensory pathways and specific olfactory cues that modulate aging are unknown. Here, we show that the olfactory receptor for carbon dioxide, Gustatory Receptor 63a (Gr63a), plays a role in determining longevity in Drosophila melanogaster. Flies lacking Gr63a function live longer, have increased fat storage, and exhibit greater reproductive output than control flies. Ablation of the neurons that express Gr63a also results in long-lived flies. Notably, the smell of live yeast does not affect the lifespan of flies that lack a functional Gr63a receptor, which suggests that carbon dioxide is a key regulatory molecule of this complex odor. Because Gr63a expression is restricted to a very select population of neurons, these results implicate a specific neural circuit in the modulation of fly lifespan.
Brachypodium distachyon (Brachypodium) is a model for the temperate grasses which include important cereals such as barley, wheat and oats. Comparison of the Brachypodium genome (accession Bd21) with those of the model dicot Arabidopsis thaliana and the tropical cereal rice (Oryza sativa) provides an opportunity to compare and contrast genetic pathways controlling important traits. We analysed the homologies of genes controlling the induction of flowering using pathways curated in Arabidopsis Reactome as a starting point. Pathways include those detecting and responding to the environmental cues of day length (photoperiod) and extended periods of low temperature (vernalization). Variation in these responses has been selected during cereal domestication, providing an interesting comparison with the wild genome of Brachypodium. Brachypodium Bd21 has well conserved homologues of circadian clock, photoperiod pathway and autonomous pathway genes defined in Arabidopsis and homologues of vernalization pathway genes defined in cereals with the exception of VRN2 which was absent. Bd21 also lacked a member of the CO family (CO3). In both cases flanking genes were conserved showing that these genes are deleted in at least this accession. Segmental duplication explains the presence of two CO-like genes in temperate cereals, of which one (Hd1) is retained in rice, and explains many differences in gene family structure between grasses and Arabidopsis. The conserved fine structure of duplications shows that they largely evolved to their present structure before the divergence of the rice and Brachypodium. Of four flowering-time genes found in rice but absent in Arabidopsis, two were found in Bd21 (Id1, OsMADS51) and two were absent (Ghd7, Ehd1). Overall, results suggest that an ancient core photoperiod pathway promoting flowering via the induction of FT has been modified by the recruitment of additional lineage specific pathways that promote or repress FT expression.
The wax layer covering the insect's cuticle plays an important protective role, as for example, uncontrolled water loss. In social insects, wax production is well-known in some bees that use it for nest building. Curiously, mated-fertile queens of the ant Ectatomma tuberculatum produce an uncommon extra-wax coat and, consequently queens (mated-fertile females) are matte due to such extra cuticular hydrocarbon (CHC) coat that covers the cuticle and masks the brightness of the queens' cuticle while gynes (virgin-infertile queens) are shiny. In this study, histological analysis showed differences in the epidermis between fertile (i.e., queens or gynes with highly ovarian activity) and infertile females (gynes or workers with non developed ovaries). In fertile females the epidermis is a single layer of cubic cells found in all body segments whereas in infertile females it is a thin layer of flattened cells. Ultrastructural features showed active secretory tissue from fertile females similar to the glandular epithelium of wax-producing bees (type I gland). Different hypotheses related to the functions of the glandular epithelium exclusive to the E. tuberculatum fertile queens are discussed.
In order to test how gravitational information would affect the choice of stable reference frame used to control posture and voluntary movement, we have analysed the forearm stabilisation during sit to stand movement under microgravity condition obtained during parabolic flights. In this study, we hypothesised that in response to the transient loss of graviceptive information, the postural adaptation might involve the use of several strategies of segmental stabilisation, depending on the subject's perceptual typology (dependence - independence with respect to the visual field). More precisely, we expected a continuum of postural strategies across subjects with 1) at one extreme the maintaining of an egocentric reference frame and 2) at the other the re-activation of childhood strategies consisting in adopting an egocentric reference frame. To check this point, a forearm stabilisation task combined with a sit to stand movement was performed with eyes closed by 11 subjects during parabolic flight campaigns. Kinematic data were collected during 1-g and 0-g periods. The postural adaptation to microgravity's constraint may be described as a continuum of strategies ranging from the use of an exo- to an egocentric reference frame for segmental stabilisation. At one extremity, the subjects used systematically an exocentric frame to control each of their body segments independently, as under normogravity conditions. At the other, the segmental stabilisation strategies consist in systematically adopting an egocentric reference frame to control their forearm's stabilisation. A strong correlation between the mode of segmental stabilisation used and the perceptual typology (dependence - independence with respect to the visual field) of the subjects was reported. The results of this study show different subjects' typologies from those that use the forearm orientation in a mainly exocentric reference frame to those that use the forearm orientation in a mainly egocentric reference frame.
Little is known about the reasoning mechanisms used by physicians in decision-making and how this compares to diagnostic clinical practice guidelines. We explored the clinical reasoning process in a real life environment. This is a qualitative study evaluating transcriptions of sixteen physicians' reasoning during appointments with patients, clinical discussions between specialists, and personal interviews with physicians affiliated to a hospital in Brazil. Four main themes were identified: simple and robust heuristics, extensive use of social environment rationality, attempts to prove diagnostic and therapeutic hypothesis while refuting potential contradictions using positive test strategy, and reaching the saturation point. Physicians constantly attempted to prove their initial hypothesis while trying to refute any contradictions. While social environment rationality was the main factor in the determination of all steps of the clinical reasoning process, factors such as referral letters and number of contradictions associated with the initial hypothesis had influence on physicians' confidence and determination of the threshold to reach a final decision. Physicians rely on simple heuristics associated with environmental factors. This model allows for robustness, simplicity, and cognitive energy saving. Since this model does not fit into current diagnostic clinical practice guidelines, we make some propositions to help its integration.
Health Diplomacy and the Enduring Relevance of Foreign Policy Interests:
The rise of global health issues within the world of foreign policy is precipitating great interest in the concept and practice of health diplomacy. Much discussion of this new field, particularly within the global health community, has narrowly focused on how diplomatic negotiations and foreign policy can be used to support global health goals [1],[2]. Recent articles claim, for example, that "foreign policy is now being driven substantially by health" [3], and that health can move "foreign policy away from a debate about interests to one about global altruism" [4].
Landscape Genetics Reveals Focal Transmission of a Human Macroparasite:
Currently, knowledge of transmission patterns of human helminth parasites is based on traditional epidemiological data such as the number of parasites within hosts. Genetic markers can greatly facilitate our understanding of the transmission process because they provide an indirect means to infer dispersal. Here, we apply novel landscape genetics methods to examine the transmission dynamics of the world's most common human macroparasite, Ascaris lumbricoides. Specifically, we tested for both the presence of multiple transmission foci in a single human village in Nepal and the epidemiological factors associated with such infection foci. On this very local scale, we were surprised to find multiple transmission foci that were centered on households and that reinfections were occurring from the same foci. Thus, our study illustrates the utility of population genetics analyses in epidemiology. Furthermore, our study challenges current dogma by revealing fragmentation of transmission rather than homogeneous parasite mixing within a single human community. Thus, the results have important implications for drug resistance evolution and parasite control.
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