Living on predictability: modelling the density distribution of efficient foraging seabirds

In areas with regular fishing coastal fleets seabirds may benefit from the predictability of discards from fishing vessels, but it is not clear to what extent birds rely on this predictable resource and whether foraging is synchronized with the diel availability of discards. In this paper we investigate if a typical scavenger species, the yellow‐legged gull Larus michahellis, takes advantage of the temporal and spatial predictability of fish discards in the western Mediterranean Sea. The activity and distribution of the trawling fleet in this area is regulated and very predictable in time and space. We gathered aerial survey data across a relatively large area close to the coast to study the spatial distribution and density of L. michahellis, and modelled the density distribution of the species in relation to several oceanographic, ecological and temporal variables, using two different modelling approaches: MARS (multivariate adaptative regression splines) and GLM (generalized linear models). Our models suggest that the spatial density of trawlers at sea and the time of the day are the best explanatory variables of gull distribution, and that gulls concentrate in areas with vessels mainly during fish discarding time, supporting the hypothesis that gulls optimize time foraging to take advantage of fishery waste predictability. Additional surveys from the main gull roosting sites inshore support this hypothesis, as gulls start leaving to the sea just before fishing is completed and vessels begin discarding fish scraps when back to the harbour. This study represents one of the few examples of applying MARS to density distribution modelling, although its application to marine ecosystems should be conducted with caution because of large areas with real absence data. GLMs have shown to be more adaptable to such kind of data. Our data confirm the importance of fishery waste for L. michahellis, not only as a food resource but also as a major driver of their activity and distribution patterns. The ability of seabirds to predict accurately when a food resource will be available implies that modelling their distribution at sea needs to include such variables, both in spatial and temporal dimensions.     

Is Chytridiomycosis an Emerging Infectious Disease in Asia?

The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused dramatic amphibian population declines and extinctions in Australia, Central and North America, and Europe. Bd is associated with >200 species extinctions of amphibians, but not all species that become infected are susceptible to the disease. Specifically, Bd has rapidly emerged in some areas of the world, such as in Australia, USA, and throughout Central and South America, causing population and species collapse. The mechanism behind the rapid global emergence of the disease is poorly understood, in part due to an incomplete picture of the global distribution of Bd. At present, there is a considerable amount of geographic bias in survey effort for Bd, with Asia being the most neglected continent. To date, Bd surveys have been published for few Asian countries, and infected amphibians have been reported only from Indonesia, South Korea, China and Japan. Thus far, there have been no substantiated reports of enigmatic or suspected disease-caused population declines of the kind that has been attributed to Bd in other areas. In order to gain a more detailed picture of the distribution of Bd in Asia, we undertook a widespread, opportunistic survey of over 3,000 amphibians for Bd throughout Asia and adjoining Papua New Guinea. Survey sites spanned 15 countries, approximately 36° latitude, 111° longitude, and over 2000 m in elevation. Bd prevalence was very low throughout our survey area (2.35% overall) and infected animals were not clumped as would be expected in epizootic events. This suggests that Bd is either newly emerging in Asia, endemic at low prevalence, or that some other ecological factor is preventing Bd from fully invading Asian amphibians. The current observed pattern in Asia differs from that in many other parts of the world.     

The cytoskeleton, a structure that is susceptible to the toxic mechanism activated by palytoxins in human excitable cells

Palytoxin is a marine toxin responsible for a fatal type of poisoning in humans named clupeotoxism, with symptoms such as neurologic disturbances. It is believed that it binds to the Na(+)/K(+)-ATPase from the extracellular side and modifies cytosolic ions; nevertheless, its effects on internal cell structures, such as the cytoskeleton, which might be affected by these initial events, have not been fully elucidated. Likewise, ostreocin-D, an analog of palytoxin, has been only recently found, and its action on excitable cells is therefore unknown. Therefore, our aim was to investigate the modifications of ion fluxes associated with palytoxin and ostreocin-D activities, and their effects on an essential cytoskeletal component, the actin system. We used human neuroblastoma cells and fluorescent dyes to detect changes in membrane potential, intracellular Ca(2+) concentration, cell detachment, and actin filaments. Fluorescence values were obtained with spectrofluorymetry, laser-scanning cytometry, and confocal microscopy; the last of these was also used for recording images. Palytoxin and ostreocin-D modified membrane permeability as a first step, triggering depolarization and increasing Ca(2+) influx. The substantial loss of filamentous actin, and the morphologic alterations elicited by both toxins, are possibly secondary to their action on ion channels. The decrease in polymerized actin seemed to be Ca(2+)-independent; however, this ion could be related to actin cytoskeletal organization. Palytoxin and ostreocin-D alter the ion fluxes, targeting pathways that involve the cytoskeletal dynamics of human excitable cells.     

New evidence for parallel evolution of colour patterns in Malagasy poison frogs (Mantella)

Malagasy poison frogs of the genus Mantella are diurnal and toxic amphibians of highly variable and largely aposematic coloration. Previous studies provided evidence for several instances of homoplastic colour evolution in this genus but were unable to sufficiently resolve relationships among major species groups or to clarify the phylogenetic position of several crucial taxa. Here, we provide cytochrome b data for 143 individuals of three species in the Mantella madagascariensis group, including four newly discovered populations. Three of these new populations are characterized by highly variable coloration and patterns but showed no conspicuous increase of haplotype diversity which would be expected under a scenario of secondary hybridization or admixture of chromatically uniform populations. Several populations of these variable forms and of M. crocea were geographically interspersed between the distribution areas of Mantella aurantiaca and Mantella milotympanum. This provides further support for the hypothesis that the largely similar uniformly orange colour of the last two species evolved in parallel. Phylogenies based on over 2000 bp of two nuclear genes (Rag-1 and Rag-2) identified reliably a clade of the Mantella betsileo and Mantella laevigata groups as sister lineage to the M. madagascariensis group, but did not support species within the latter group as monophyletic. The evolutionary history of these frogs might have been characterized by fast and recurrent evolution of colour patterns, possibly triggered by strong selection pressures and mimicry effects, being too complex to be represented by simple bifurcating models of phylogenetic reconstruction.     

Development of a F actin-based live-cell fluorimetric microplate assay for diarrhetic shellfish toxins

A new cytotoxicity assay for detection and quantitation of diarrhetic shellfish toxins (DSP) is presented. This assay is based upon fluorimetric determination of F-actin depolymerization induced by okadaic acid (OA)-class compounds in the BE(2)-M17 neuroblastoma cell line. No interferences were observed with other marine toxins such as saxitoxin, domoic acid, or yessotoxin, thus indicating a good specificity of the assay as expected by the direct relationship between protein phosphatase inhibition and cytoskeletal changes. The proposed method is rapid (<2h) and shows a linear response in the range of 50-300 nM OA. The detection limit of the assay for crude methanolic extracts of bivalves lies between 0.2 and 1.0 microg OA per gram of digestive glands, depending on the type of samples (fresh or canned), thus being similar to that of the mouse bioassay. The performance of this assay has been evaluated by comparative analysis of 32 toxic mussel samples by the F-actin assay, mouse bioassay, HPLC and PP2A inhibition assay. Results obtained by the F-actin method showed no differences with HPLC and significant correlation with PP2A inhibition assay (r(2)=0.71). No false negative results were obtained with this new cell assay, which also showed optimum reproducibility.     

Potent in vitro anti-Trypanosoma cruzi activity of pyridine-2-thiol N-oxide metal complexes having an inhibitory effect on parasite-specific fumarate reductase

In the search for new therapeutic tools against Chagas disease (American trypanosomiasis) palladium and platinum complexes of the bioactive ligand pyridine-2-thiol N-oxide were exhaustively characterized and evaluated in vitro. Both complexes showed high in vitro growth inhibition activity (IC(50) values in the nanomolar range) against Trypanosoma cruzi, the causative agent of the disease. They were 39-115 times more active than the antitrypanosomal drug Nifurtimox. The palladium complex showed an approximately threefold enhancement of the activity compared with the parent compound. In addition, owing to their low unspecific cytotoxicity on mammalian cells, the complexes showed a highly selective antiparasite activity. To get an insight into the mechanism of action of these compounds, DNA, redox metabolism (intraparasite free-radical production) and two parasite-specific enzymes absent in the host, namely, trypanothione reductase and NADH-fumarate reductase, were evaluated as potential parasite targets. Additionally, the effect of metal coordination on the free radical scavenger capacity previously reported for the free ligand was studied. All the data strongly suggest that trypanocidal action of the complexes could mainly rely on the inhibition of the parasite-specific enzyme NADH-fumarate reductase.