Résumé
Population genetic studies are efficient for inferring the invasion history based on acomparison of native and invasive populations, especially when conducted at speciesscale. An expected outcome in invasive populations is variability loss, and this is especiallytrue in self-fertilizing species. We here focus on the self-fertilizing Pseudosuccineacolumella, an invasive hermaphroditic freshwater snail that has greatly expandedits geographic distribution and that acts as intermediate host of Fasciola hepatica, thecausative agent of human and veterinary fasciolosis. We evaluated the distribution ofgenetic diversity at the largest geographic scale analysed to date in this species by surveying80 populations collected during 16 years from 14 countries, using eight nuclearmicrosatellites and two mitochondrial genes. As expected, populations from NorthAmerica, the putative origin area, were strongly structured by selfing and history andharboured much more genetic variability than invasive populations. We found highselfing rates (when it was possible to infer it), none-to-low genetic variability andstrong population structure in most invasive populations. Strikingly, we found aunique genotype/haplotype in populations from eight invaded regions sampled allover the world. Moreover, snail populations resistant to infection by the parasite aregenetically distinct from susceptible populations. Our results are compatible withrepeated introductions in South America and flash worldwide invasion by this uniquegenotype/haplotype. Our study illustrates the population genetic consequences of bio-logical invasion in a highly selfing species at very large geographic scale. We discusshow such a large-scale flash invasion may affect the spread of fasciolosis