My scientific interests mainly deal with molecular evolution, population genetics and speciation in a geographical context. My PhD thesis focuses on a genus of hairy land snails, Trochulus spp. (formerly known as Trichia), in which the species' taxonomical status has been an issue much debated. Morphologically, most uncertainties are explained by the strong plasticity of the individuals in response to the environment: individuals from different species will look similar just because they live in similar habitats. On the other hand, the genetic puzzle might date back to the glaciations. Indeed, as well as many other species' populations, land snails got repetitively isolated, diverged and subsequently came into secondary contact. As a result, some of these land snail species have extremely unclear boundaries, with individuals often similar morphologically but genetically very divergent... or the contrary! My project aims at a better understanding of the patterns of post glacial recolonisation of Switzerland by these land snails, as well as investigating the mechanisms behind. I focus on two species within the genus Trochulus. With T. villosus, I try to figure out the recolonisation history of this species at the scale of Switzerland (phylogeographical approach) and at a local scale in the Jura, VD (population genetics). With T. sericeus, I investigate the population genetics of this species presumably covering in fact several cryptic species. If T. sericeus indeed is a complex of undistinguished species, I expect the observed divergence on the mitochondrial DNA to correlate with a reduced nuclear geneflow, indicative of some reproductive isolation. I study this along a transect following the Sarine (Gruyère, FR).