Laurence Mouton

Variable-number tandem repeats (VNTRs) have been identified in populations of Pasteuria ramosa , a castrating endobacterium of Daphnia species. The allelic polymorphisms at 14 loci in laboratory and geographically diverse soil samples showed that VNTRs may serve as biomarkers for the genetic characterization of P. ramosa isolates.

Regulation of microbial population density is a necessity in stable symbiotic interactions. In Wolbachia symbiosis, both bacterial and host genotypes are involved in density regulation, but environmental factors may also affect bacterial population density. Here, we studied the interaction between three strains of Wolbachia in two divergent homozygous lines of the wasp Leptopilina heterotoma at two different temperatures. Wolbachia density varied between the two host genotypes at only one temperature. Moreover, at this temperature, reciprocal-cross F1 insects displayed identical Wolbachia densities, which were intermediate between the densities in the two parental lines. While these findings confirm that the host genotype plays an important role in Wolbachia density, they also highlight its interaction with environmental conditions, making possible the evolution of local adaptations for the regulation of Wolbachia density.

The outcome and the evolution of host-symbiont associations depend on environmental constraints, but responses are difficult to predict since they arise from a complex interaction between the host, the parasite and the environment. The situation can be even more complex when multiple parasite genotypes, with potentially different responses to environmental changes, coexist within a single host. In this paper, we investigated the effect of the temperature (from 14 to 26 °C) during the host development on the density of 3 strains of the intracellular bacteriumWolbachiathat coexist within the waspLeptopilina heterotoma. In this species,Wolbachiainduces cytoplasmic incompatibility, a sperm-egg incompatibility that allows it to spread and persist in host populations. Using real-time quantitative PCR we found that (i)Wolbachiadensity is temperature-specific and highest at 26 °C; (ii) the order of the abundance of the 3Wolbachiastrains does not vary with temperature changes; (iii) the response of bacterial density to temperature occurs within a single insect generation, during the egg-to-adult developmental period; (iv) in this species, temperature-related changes inWolbachiadensity do not influence cytoplasmic incompatibility.