Search

Genetic structure, i.e. intra-population genetic diversity and inter-population genetic differentiation, is influenced by the amount and spatial configuration of habitat. Measuring the amount of reachable habitat (ARH) makes it possible to describe habitat patterns by considering intra-patch and inter-patch connectivity, dispersal capacities and matrix resistance. Complementary ARH metrics computed under various resistance scenarios are expected to reflect both drift and gene flow influence on genetic structure. Using an empirical genetic dataset concerning the large marsh grasshopper (Stethophyma grossum), we tested whether ARH metrics are good predictors of genetic structure. We further investigated (i) how the components of the ARH influence genetic structure and (ii) which resistance scenario best explains these relationships. We computed local genetic diversity and genetic differentiation indices in genetic graphs, and ARH metrics in the unified and flexible framework offered by landscape graphs, and we tested the relationships between these variables. ARH metrics were relevant predictors of the two components of genetic structure, providing an advantage over commonly used habitat metrics. Although allelic richness was significantly explained by three complementary ARH metrics in the best PLS regression model, private allelic richness and MIW indices were essentially related with the ARH measured outside the focal patch. Considering several matrix resistance scenarios was also key for explaining the different genetic responses. We thus call for further use of ARH metrics in landscape genetics to explain the influence of habitat patterns on the different components of genetic structure.

Porcellionides pruinosus is a cosmopolitan woodlouse. It is known to exhibit patterns of geographical variation between populations, and has been suspected to consist of several very closely related species. This species was found to carry Wolbachia endosymbionts, alpha-proteobacteria which are known to modify the reproduction of their crustacean hosts by inducing cytoplasmic incompatibility or feminization. In the P. pruinosus complex, Wolbachia induced feminization, but two different patterns of infection were reported: high prevalence and presence of infected males, or low prevalence and absence of infected males. In this study we investigated nine populations described as Porcellionides pruinosus carrying different Wolbachia strains, with the aim of investigating the possibility of coevolution between symbionts and hosts. Molecular analyses were carried out on both Wolbachia DNA (wsp gene) and host mitochondrial DNA (mt LSU rDNA). We show that (1) the nine host populations exhibited a high genetic differentiation so that they have to be split into two sibling species; (2) three different Wolbachia strains were found in the host complex but were not species-specific; and (3) the pattern of infection by Wolbachia was more host-dependent than symbiont-dependent.

Wolbachia bacteria are vertically transmitted endosymbionts that disturb the reproduction of many arthropods thereby enhancing their spread in host populations. Wolbachia are often responsible for changes of sex ratios in terrestrial isopods, a result of the feminization of genotypic males. Here we found that the Wolbachia hosted by Cylisticus convexus (wCc) caused unidirectional cytoplasmic incompatibility (CI), an effect commonly found in insects. To understand the diversity of Wolbachia-induced effects in isopods, wCc were experimentally transferred in a novel isopod host, Armadillidium vulgare. wCc conserved the ability to induce CI. However, Wolbachia were not transmitted to the eggs, so the capacity to restore the compatibility in crosses involving two transinfected individuals was lost. The feminizing Wolbachia hosted by A. vulgare was unable to rescue CI induced by wCc. These results showed that Wolbachia in isopods did not evolved broadly to induce feminization, and that CI and the feminizing effect are probably due to different mechanisms. In addition, wCc reduces the mating capacity of infected C. convexus males, suggesting that the bacteria might alter reproductive behaviour. The maintenance of wCc in host populations is discussed.

International audience; In Culex pipiens mosquitoes, resistance to organophosphorous insecticides often results from increased detoxification by two types of esterases, A and B, which are closely linked. Overproduction of all esterases B so far investigated (B1, B2, B4, B5 and B6) is from gene amplification. An esterase A gene (esterase A2) has recently been cloned from mosquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences of three additional esterase genes from insecticide-resistant strains of Culex pipiens originating from France and California which show at least 93 per cent homology with the esterase A2 gene sequence. Restriction enzyme mapping shows that the esterase A gene lies within 2.2 kb of the esterase B gene. In mosquitoes with overproduced esterases A2 and B2, the amplification level of esterase A is equal to that of esterase B suggesting that the genes are coamplified. Furthermore, we show that in one strain with an overproduced A esterase (A1), gene amplification cannot account for the increased protein level. This indicates that overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism - the nature of which remains to be identified.