Differential tolerance of body fluid dilution in two species of tropical hermit crabs: not due to osmotic/ionic regulation

The tropical intertidal hermit crabs Clibanarius taeniatus and Clibanarius virescens were examined for differences in survival and physiological responses in low salinity. We found that C. taeniatus survived better in dilute seawater than C. virescens and that these species did not differ in their abilities to regulate haemolymph osmolarity, ionic concentration of the haemolymph or body fluid volume. We also found no difference in oxygen consumption between the species when acutely exposed to a range of temperature and salinity combinations. It is concluded that the greater survival in dilute seawater by C. taeniatus compared to C. virescens is due to a greater tolerance of dilution of body fluids by C. taeniatus. Differences in tolerance to dilute seawater may influence the habitat preferences of these species within the same geographical area.     

Structure of biological solar energy converters - further revelations

Photosynthetic organisms harvest solar energy by absorbing light and ultimately transferring energy through a cascade of chemical reactions to power all cellular processes. Core components initiating this reaction cascade are the photosynthetic reaction centres Photosystem I and Photosystem II. Two recent publications on the structure of the reaction centres by Adam Ben-Shem et al. and Kristina Ferreira et al. represent a big step towards understanding the evolutionary development of the core energy conversion process and identifying the site of the water oxidation process, the source of atmospheric oxygen.     

Public, private and non-specific antibodies induced by non-cytopathic viral infections

Lymphocytic choriomeningitis virus (LCMV) represents a useful experimental model of murine infection with a non-cytopathic virus, bearing resemblance to HIV and hepatitis C virus (HCV) infections in humans. Recent data from the LCMV model indicate that the humoral immune response that is induced by non-cytopathic viruses is far more complex than previously appreciated. LCMV-induced IgG production is largely polyclonal, with more than 90% of the antibody repertoire constituting non-relevant specificities. A delayed virus-neutralizing antibody response is induced, including specificities directed not only against the parental LCMV-strain present in the host but also cross-specifically against LCMV-variants isolated from other hosts. These findings provide novel insights to aid our understanding of clinically relevant observations that are recorded following human infection with HIV, HCV and dengue viruses.     

Missorting of LaCrosse virus nucleocapsid protein by the interferon-induced MxA GTPase involves smooth ER membranes

The interferon-induced human MxA protein belongs to the class of dynamin-like, large guanosine-5'-triphosphatases that are involved in intracellular vesicle trafficking and organelle homeostasis. MxA shares many properties with the other members of this protein superfamily, including the propensity to self-assemble and to associate with lipid membranes. However, MxA is unique in that it has antiviral activity and inhibits the replication of several RNA viruses. Here, we determined the role of membranes for the antiviral function of MxA using LaCrosse-bunyavirus (LACV). We show that MxA does not affect trafficking and sorting of viral glycoproteins but binds and mislocates the viral nucleocapsid (N) protein into membrane-associated, large perinuclear complexes. We further demonstrate that MxA localizes to a subcompartment of the smooth endoplasmic reticulum where the viral N protein accumulates. In infected MxA-expressing cells, oligomeric MxA/N complexes are formed in close association with COP-I-positive vesicular-tubular membranes. Our results suggest that this membrane compartment is the preferred place where MxA and N interact, leading to efficient sequestration and missorting of an essential viral component.     

Southern Sea Otter as a Sentinel of Marine Ecosystem Health

The southern sea otter (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act (ESA) and is a keystone species, strongly influencing the abundance and diversity of the other species within its kelp forest ecosystem. This is accomplished primarily by preying upon urchins that eat the kelp stipe and holdfast, which can reduce a kelp forest to an urchin barren. Sea otters are very susceptible to marine pollutants such as petroleum, which may be directly toxic and/or alter their furs insulating properties. Sea otters are an excellent sentinel species. They eat approximately 25% of their body weight per day in shellfish and other invertebrates, and can concentrate and integrate chemical contaminants. In addition, they appear to be susceptible to a number of diseases and parasites that may have anthropogenic origins, and shellfish may serve as an intermediary for some of these infections. Many of the shellfish the otters eat are also harvested for human food. In their role as sentinels, sea otter health has implications for human health, economic sustainability of shellfisheries, as well as overall marine ecosystem health. The recent southern sea otter decline has been viewed with some alarm by conservationists and, indeed, recovery seems a long way off. High mortality rather than depressed recruitment appears to underlie the decline. A good deal of debate has centered on the role of infectious diseases and parasites, exposure to contaminants, nutrition and prey availability, net and pot fishery interactions, and other sources of mortality. Current research is being done related to major classes of mortality, various types of pollutants and some specific organisms causing southern sea otter mortality, and their implications for marine ecosystem health and sustainability.     

Bayesian analysis of binary prediction tree models for retrospectively sampled outcomes

Classification tree models are flexible analysis tools which have the ability to evaluate interactions among predictors as well as generate predictions for responses of interest. We describe Bayesian analysis of a specific class of tree models in which binary response data arise from a retrospective case-control design. We are also particularly interested in problems with potentially very many candidate predictors. This scenario is common in studies concerning gene expression data, which is a key motivating example context. Innovations here include the introduction of tree models that explicitly address and incorporate the retrospective design, and the use of nonparametric Bayesian models involving Dirichlet process priors on the distributions of predictor variables. The model specification influences the generation of trees through Bayes' factor based tests of association that determine significant binary partitions of nodes during a process of forward generation of trees. We describe this constructive process and discuss questions of generating and combining multiple trees via Bayesian model averaging for prediction. Additional discussion of parameter selection and sensitivity is given in the context of an example which concerns prediction of breast tumour status utilizing high-dimensional gene expression data; the example demonstrates the exploratory/explanatory uses of such models as well as their primary utility in prediction. Shortcomings of the approach and comparison with alternative tree modelling algorithms are also discussed, as are issues of modelling and computational extensions.     

Multi-tasking by the p75 neurotrophin receptor: sortilin things out?

Signalling by the p75 neurotrophin receptor has been implicated in diverse neuronal responses, including increased differentiation or survival, inhibition of regeneration, and initiation of apoptotic cell death. These numerous roles are matched by, but are not yet correlated with, a multiplicity of extracellular ligands and intracellular interactors. Membrane proteins such as sortilin, a member of the Vps10p family of sorting receptors, and the glycosylphosphatidylinositol-linked Nogo receptor (NgR) and the associated adaptor lingo 1 have recently been added to the list of p75-interacting modulators. Other studies have described intramembranal cleavage of p75 and the potential nuclear targeting of cleavage fragments or of the complete receptor after it has been internalized into a putative signalling endosome. These findings suggest that some of the diversity in p75 activities might be due to differential subcellular localization and transport of p75 receptor complexes. We therefore argue that cell-biology-driven approaches are now required to make sense of p75 signalling.     

The influence of contests on optimal clutch size: a game-theoretic model

We develop a game-theoretic model to predict the effect of size-dependent contest outcomes on optimal-clutch-size decisions. We consider the case where larger individuals develop from smaller clutches and, as adults, are advantaged in competition for limiting resources. The relationship between fitness and size thus depends on the sizes of other members of the population. We show that clutch-size optima are decreased by body-size-dependent contest outcomes, with larger effects when body size is most affected by clutch size, when prior resource ownership has less influence on contest outcome and when contests occur more frequently. We also show the existence of polymorphisms in clutch-size optima and that clutch-size driven changes in population density can, via an effect on the probability of host finding, further influence optimal clutch size. Our model is formulated to match the life history of a parasitoid wasp, in which clutch size affects offspring size and females engage in direct contests for host ownership, which larger females tend to win; we confirm that female-female competition is likely to influence clutch size in this species. However, the model is also relevant to clutch size in other taxa and supports recent suggestions concerning reproductive decisions in great tits.