Kerguelen, un observatoire scientifique dans le Grand Sud.

8 pagesNational audienc

Acidic shell proteins of the Mediterranean fan mussel Pinna nobilis.

43 pagesIn molluscs, the shell secretion process is controlled by a set of extracellular macromolecules collectively called the shell matrix. The shell matrix, which is produced by the mantle epithelial cells during mineralization, is predominantly composed of proteins, glycoproteins, acidic polysaccharides, and chitin that precisely regulate the deposition of calcium carbonate outside the mantle cells. In the present paper, we focus on the shell of Pinna nobilis, the giant Mediterranean fan mussel, usually considered as a model for studying molluscan biomineralization processes. P. nobilis exhibits indeed a nacro-prismatic shell, the outer layer of which is constituted of the so-called "regular simple calcitic prisms," according to Carter and Clark (1985). We review here the microstructural characteristics of the prisms and nacre and the biochemical properties of their associated matrices. In particular, the calcitic prisms of P. nobilis are characterized by a cortege of unusually acidic intraprismatic proteins, while the ones of the nacreous layer seem less acidic. A brief description of the molecular characterization of three acidic proteins, caspartin, calprismin and mucoperlin, is given. In particular, we show that extremely acidic intracrystalline proteins such as caspartin interact with calcium carbonate at different scales, from micrometric to crystal lattice levels

Infection by a vertically-transmitted microsporidian parasite is associated with a female-biased sex ratio and survival advantage in the amphipod Gammarus roeseli.

5 pagesInternational audienceVertically transmitted parasites may have positive, neutral or negative effects on host fitness, and are also predicted to exhibit sex-specific virulence to increase the proportion or fitness of the transmitting sex. We investigated these predictions in a study on the survival and sex ratio of offspring of the amphipod Gammarus roeseli from females infected by the vertically transmitted microsporidia Nosema granulosis. We found, to our knowledge, the first evidence for a positive relationship between N. granulosis infection and host survival. Infection was associated with sex ratio distortion, not by male-killing, but probably by parasite-induced feminization of putative G. roeseli males. This microsporidia also feminizes another amphipod host, Gammarus duebeni, which is phylogenetically and biogeographically distant from G. roeseli. Our study suggests that the reproductive system of gammarids is easily exploited by these vertically-transmitted parasites, although the effects of infections on host fitness may depend on specific host-parasite species interactions

Dynamics of PHA-induced immune response and plasma carotenoids in birds: should we have a closer look?

8 pagesInternational audienceAllocation trade-offs of limited resources are thought to ensure the honesty of sexual signals and are often studied using controlled immune challenges. One such trade-off between immunity and ornaments is that involving carotenoids. Phytohemagglutinin (PHA)-induced immune response is a widely used immune challenge, yet more details on the underlying physiological mechanisms and potential costs are needed. We investigated the temporal dynamics of PHA-induced immune response and associated changes in blood carotenoids, body mass and a carotenoid-based coloured signal. We found variation in individual response patterns to PHA after peak swelling was reached, with birds showing either a rapid or a slow subsequent decrease in swelling, suggesting variation in the duration of the immune response and/or inflammation. Body mass did not affect immune response. Plasma carotenoids followed a transient decrease closely matching the dynamics of the swelling. The peak of the immune response was negatively related to initial plasma carotenoid levels and positively correlated to the relative decrease in plasma carotenoids. Individual variation in duration of the swelling could be partly explained by plasma carotenoids; high initial carotenoid levels were associated with a slower decrease of the swelling. These contradictory effects of carotenoids suggest a complex role in the immune response. Bill colour was positively correlated to initial plasma carotenoid concentration but it did not predict or change as a consequence of immune response to PHA. Bill colour thus reflects medium- or long-term quality rather than immediate quality. Taking into account the dynamics of the immune response and that of associated physiological parameters would thus yield new insights into our interpretation of variation in PHA response

Adult survival selection in relation to multilocus heterozygosity and body size in a tropical bird species, the Zenaida dove, Zenaida aurita.

10 pagesInternational audienceBoth phenotypic and genetic quality can influence the survival of individuals through time, although their relative influences are rarely addressed simultaneously. Here we used capture-mark-recapture modelling to assess the influence of both multilocus heterozygosity (MLH) and body size on apparent adult survival in a tropical bird species, the Zenaida dove, Zenaida aurita, using a sample of 391 individuals genotyped at 11 microsatellites, while controlling for the effects of sex. No effect of body size on either adult survival or capture rate was found. In the best model, survival was a logit linear function of MLH, whereas detection probability was a sex-dependent logit linear function of the logarithm of field effort, increasing with time and affected by a random individual effect. Using a Bayesian approach, we found that MLH explained 1.14 % of the total deviance, as expected from theory and previous studies of heterozygosity-fitness correlations, with no evidence for local effects. However, results from capture-mark-recapture modelling indicated that expected longevity varied from 4.8 years in the least heterozygous individuals (MLH = 0.37) to 10.6 years in the most heterozygous ones (MLH = 1), thus suggesting that MLH had potentially a substantial effect on survival. We discuss our results in relation to current hypotheses about the origin of heterozygosity-fitness correlations

Coloration reflects behavioural types in the convict cichlid, Amatitlania siquia.

9 pagesInternational audienceInterindividual behavioural differences, consistent over time and across situations, are frequently related to differences in reproductive success, susceptibility to disease and competitive ability. The behavioural phenotype of a conspecific is likely to affect the outcome of a social interaction, so an individual must be able to accurately assess behavioural phenotypes in order to optimize behavioural responses during mate choice, cooperative relationships and agonistic interactions. However, behavioural assessment based on dyadic interactions in different contexts can be costly because it may require significant time, increase the risk of predation and often necessitates special cognitive abilities. Different colour cues are associated with different life history strategies in many species, so coloration might also correlate with behavioural phenotype. Thus, conspecifics could use coloration as a single cue for the mediation of social interactions. We investigated the relationship between personality and coloration in the monogamous, biparental convict cichlid. This species has black melanin-based stripes with interindividual variation in the intensity of these stripes. In addition, females have bright orange spots on their abdomens. Using repeatable measures of boldness, exploration and aggressiveness, we were able to define a behavioural syndrome and quantified the behavioural type of each individual. Behavioural types were predicted by colour traits. In particular, proactive individuals (more aggressive, bolder and quicker to resume behaviour after being startled) were more likely to be dark and, among females, have smaller orange areas. Our results support the hypothesis that coloration in the convict cichlid is related to personality. Thus, coloration could play an important role in mediating social interactions, allowing a quick and reliable assessment of conspecifics' behavioural types

Habitat segregation mediates predation by the benthic fish Cottus gobio on the exotic amphipod species Gammarus roeseli.

6 pagesInternational audiencePredation is often considered as one of the most important biotic factor determining the success of exotic species. The freshwater amphipod Gammarus roeseli has widely colonized Western Europe, where it is frequently found in sympatry with the native species (Gammarus pulex). Previous laboratory experiments revealed that G. roeseli may have an advantage over G. pulex through differential predation by native fish (brown trout). Morphological anti-predator defences (spines) were found responsible for lower rates of predation on the invasive G. roeseli. Here, using both field surveys and laboratory experiments, we tested if a differential of predation exists with other fish predators naturally encountered by gammarids. The main predators present in our field site were nocturnal benthic feeders (mainly bullheads, Cottus gobio). Fish diet analysis showed that, compared to its global availability in the river, G. roeseli was less consumed than G. pulex. In the field, however, G. roeseli was found mainly in the aquatic vegetation whereas G. pulex was found in all habitat types. Laboratory experiments in microcosms revealed that G. roeseli was less prone to predation by C. gobio only when vegetation was present. Depending on the type of predator, the differential of predation could therefore be mediated by antipredator behaviour, and a better usage of refuges, rather than by morphological defences

Changement climatique et suivi de la biodiversité marine côtière aux Iles Kerguelen

International audienceNearshore marine habitats of the French sub-Antarctic islands concentrate a rich and unique biodiversity that is currently facing climate change and its still not well-understood and multifaceted effects. Understanding the impact of these changes and predicting the potential response of ecosystems requires advanced knowledge of marine life and the achievement of uninterrupted and long-term observing programs. The Proteker program, no. 1044 of the French Polar Institute Paul-Émile Victor, has been developped in partnership with the National Nature Reserve of French Southern Territories in order to establish an observatory of coastal marine biodiversity in the Kerguelen Islands and evaluate the potential effects of environmental changes. Studies are carried out at different scales, from species to community and habitat levels, through multidisciplinary approaches that include hydrographic measurements, habitat mapping and species inventories, genetic, ecophysiological, and trophic analyses. This program aims at providing nature managers with scientifi c criteria to support the production and the achievement of conservation plans.Les habitats marins côtiers des îles subantarctiques françaises concentrent une biodiversité originale qui est aujourd'hui confrontée à des changements environnementaux dont les effets sont encore mal cernés. Comprendre l'impact de ces changements et la réponse des écosystèmes implique de mieux les connaître mais aussi d'établir un suivi régulier et à long terme sur le terrain. Le programme Proteker, n°1044 de l'Institut polaire français Paul-Émile Victor, a été développé en partenariat avec la réserve naturelle nationale des Terres australes françaises dans le but d'établir un observatoire de la biodiversité marine côtière aux Îles Kerguelen et d'y évaluer l'effet des changements environnementaux. Les études sont réalisées à différentes échelles, des espèces aux communautés et aux habitats sous-marins par des approches pluridisciplinaires qui comprennent mesures hydrographiques, cartographie d'habitats et inventaires d'espèces, analyses génétiques, écophysiologiques et trophiques. Ce programme a pour ambition de fournir des critères scientifi ques aux gestionnaires de la réserve pour la mise en oeuvre des politiques de conservation et l'application des plans de gestion

Female mate choice in convict cichlids is transitive and consistent with a self-referent directional preference.

10 pagesInternational audienceINTRODUCTION: One of the most important decisions that an animal has to make in its life is choosing a mate. Although most studies in sexual selection assume that mate choice is rational, this assumption has not been tested seriously. A crucial component of rationality is that animals exhibit transitive choices: if an individual prefers option A over B, and B over C, then it also prefers A over C. RESULTS: We assessed transitivity in mate choice: 40 female convict cichlids had to make a series of binary choices between males of varying size. Ninety percent of females showed transitive choices. The mean preference index was significantly higher when a female chose between their most preferred and least preferred male (male 1 vs. male 3) compared to when they chose between males of adjacent ranks (1 vs. 2 or 2 vs. 3). The results are consistent with a simple underlying preference function leading to transitive choice: females preferred males about one third larger than themselves. This rule of thumb correctly predicted which male was preferred in 67% of the cases and the ordering in binary choices in 78% of cases. CONCLUSIONS: This study provides the first evidence for strong stochastic transitivity in a context of mate choice. The females exhibited ordinal preferences and the direction and magnitude of these preferences could be predicted from a simple rule. The females do not necessarily compare two males to choose the best; it is sufficient to use a self-referent evaluation. Such a simple decision rule has important implications for the evolution of the mating strategies and it is consistent with patterns of assortative mating repeatedly observed at population level