Restricted dispersal in a sea of gene flow.

How far do marine larvae disperse in the ocean? Decades of population genetic studies have revealed generally low levels of genetic structure at large spatial scales (hundreds of kilometres). Yet this result, typically based on discrete sampling designs, does not necessarily imply extensive dispersal. Here, we adopt a continuous sampling strategy along 950 km of coast in the northwestern Mediterranean Sea to address this question in four species. In line with expectations, we observe weak genetic structure at a large spatial scale. Nevertheless, our continuous sampling strategy uncovers a pattern of isolation by distance at small spatial scales (few tens of kilometres) in two species. Individual-based simulations indicate that this signal is an expected signature of restricted dispersal. At the other extreme of the connectivity spectrum, two pairs of individuals that are closely related genetically were found more than 290 km apart, indicating long-distance dispersal. Such a combination of restricted dispersal with rare long-distance dispersal events is supported by a high-resolution biophysical model of larval dispersal in the study area, and we posit that it may be common in marine species. Our results bridge population genetic studies with direct dispersal studies and have implications for the design of marine reserve networks.

Marine fish communities in shallow volcanic habitats.

This survey of the marine ichthyofauna of the Piton de La Fournaise volcano at Reunion Island is the first explanatory study of fish community structures in this area. It describes and analyses the main qualitative descriptors of the fish communities (i.e. species richness, diet, life history and geographical distribution) and their spatio-temporal organization. This investigation in 2011 examined lava flows of different ages, including the most recent flows that entered the ocean between 1977 and 2007. In all, 263 species belonging to 45 families were observed. Overall, the fish community was notable for an absence of top predators and a predominance of opportunistic small-bodied species, with dietary flexibility and high reproductive rates, characteristic of the early stages of ecological succession. Between-site analysis indicated that the fish assemblages differed essentially according to the intensity of the last volcanic disturbances. Fish communities in the most disturbed sites showed the highest numbers of Serranidae and the highest proportions of omnivores and small-bodied opportunistic carnivores, including a high proportion of endemic south-western Indian Ocean species. The spatial pattern of this last category of species could be the result of convergent biological traits, and their adaptation to unstable environments at the expense of their competitiveness in more biodiverse, mature communities. Conversely, fish communities in the less disturbed sites showed the highest number of Holocentridae and the highest proportion of browsers of sessile invertebrates. This last characteristic could be a consequence of higher ecological maturity, illustrated by a more specialized trophic network, for assemblages in areas with less intense disturbances. Otherwise, high structural complexity, either in unconsolidated lava boulders, rocks and rubble or high coral-covered sites, could favour the increase of the total number of species independent of disturbance intensity. Regarding the broader effects, this study helps better understand how ecosystems can resist or recover from acute disturbances and the process of ecological succession that leads to the establishment of fish communities in newly submerged habitats.

Does light explain damselfish Chromis viridis abundances observed over coral colonies?

A single autonomous video camera was used to record the abundances of Chromis viridis over a branching Acropora sp. colony eight times per day over a period of 50 days. The poor explanatory power of global radiation suggests the need for recording the light really available to the fish, especially in the UV range. The increasing number of C. viridis observed with increasing wind along shore and water level may correspond to individuals swimming further from their shelter in order to get closer to the food carried by the water currents.

Effect of various doses of deoxynivalenol on liver xenobiotic metabolizing enzymes in mice.

DON is one of the major mycotoxic contaminant of cereal grains throughout the world. The purpose of this investigation was to characterize the effects of a range of environmentally relevant doses of DON in mice exposed through a subchronic toxicological assay. Animals received 3 days per week for 4 weeks, 0.014, 0.071, 0.355 or 1.774 mg of toxin/kg b.w. All doses, except 0.014 mg/kg, provoked increases in plasma immunoglobulin A whereas there was no change in plasma biochemical parameters such as alkaline phosphatase, electrolytes or other immunoglobulins. Administration of 0.071 or 0.355 mg/kg doses led to increased liver microsomal pentoxyresorufin depentylase and cytosolic glutathione transferase activities. Examining protein modulation, western blot analyses liver fractions from mice receiving these doses revealed increased levels in both P450 2b, GST alpha and pi isoenzymes without any change in P450 1a expression. A significant competitive inhibition of deoxynivalenol on CDNB conjugation in vitro suggests that the mycotoxin is a putative substrate for glutathione S-transferases. These changes in liver xenobiotic metabolizing enzymes are discussed by considering the structural nature of deoxynivalenol and previous reports on similar effects exerted by other trichothecenes. These results suggest that a subchronic exposure to low doses of deoxynivalenol causes changes in the normal liver metabolism of xenobiotics.