Nematodes from the squeaker fishes Synodontis nigromaculatus and S. vanderwaali from the Okavango River, Botswana, including three new species

Five nematode species were recorded from the stomach and rectum of the spotted squeaker Synodontis nigromaculatus Boulenger or the finetooth squeaker S. vanderwaali Skelton & White (Mochokidae, Siluriformes) from the Okavango River, Botswana: Falcaustra similis n. sp. (Kathlaniidae), Labeonema africanum n. sp. (Cosmocercidae), Synodontisia okavangoensis n. sp. (Pharyngodonidae), Procamallanus ( Procamallanus ) laeviconchus (Wedl, 1861) (Camallanidae) and Spinitectus sp. (Cystidicolidae) (only a single female). F. similis (type-host Synodontis nigromaculatus ) differs from the similar species F. straeleni Campana-Rouget, 1961 mainly by the number and disposition of the male caudal papillae and the structure of the mouth; L. africanum (type-host S. nigromaculatus ) differs from its congeners in having distinctly longer spicules (105-120 microm), a relatively shorter gubernaculum (30-36 microm) and in the number and arrangement of the male caudal papillae; Synodontisia okavangoensis (type-host Synodontis nigromaculatus ) is characterised principally by crescent-shaped cephalic papillae, length (87 microm) and shape of the spicule as well as large eggs (0.156-0.180x69-102 microm). Synodontisia moraveci Anderson & Lim, 1996 is transferred to a newly established genus, Royandersonia n. g., (as its type-species) as R. moraveci (Anderson & Lim, 1996) n. comb. Some taxonomic problems concerning Procamallanus ( P .) laeviconchus are discussed. All species were studied by scanning electron microscopy for the first time.     

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.     

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.     

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.     

Distances that perfectly mislead

Given a collection of discrete characters (e.g., aligned DNA sites, gene adjacencies), a common measure of distance between taxa is the proportion of characters for which taxa have different character states. Tree reconstruction based on these (uncorrected) distances can be statistically inconsistent and can lead to trees different from those obtained using character-based methods such as maximum likelihood or maximum parsimony. However, in these cases the distance data often reveal their unreliability by some deviation from additivity, as indicated by conflicting support for more than one tree. We describe two results that show how uncorrected (and miscorrected) distance data can be simultaneously perfectly additive and misleading. First, multistate character data can be perfectly compatible and define one tree, and yet the uncorrected distances derived from these characters are perfectly treelike (and obey a molecular clock), only for a completely different tree. Second, under a Markov model of character evolution a similar phenomenon can occur; not only is there statistical inconsistency using uncorrected distances, but there is no evidence of this inconsistency because the distances look perfectly treelike (this does not occur in the classic two-parameter Felsenstein zone). We characterize precisely when uncorrected distances are additive on the true (and on a false) tree for four taxa. We also extend this result to a more general setting that applies to distances corrected according to an incorrect model.