Nuclear and mitochondrial genetic variability of an old invader, Dreissena polymorpha (Bivalvia), in French river basins

Analyzing non-native species after their establishment can shed light on factors responsible for their colonization success. The zebra mussel (Dreissena polymorpha), a species of Ponto-Caspian origin, is a worldwide invader, and was first reported in northern France in the nineteenth century. The genetic diversity and structure of D. polymorpha from five river basins (nine locations) in France were estimated using nuclear markers (amplified fragment length polymorphisms, AFLPs; 154 loci) and sequences from a 514 bp mitochondrial DNA region (cytochrome c oxidase subunit I; COI). Results from the two types of markers were generally congruent, although COI sequences showed limited genetic polymorphism, with one predominant and cosmopolitan haplotype (84 % of the individuals). Both COI and AFLPs revealed that the most divergent and the least polymorphic sample was the one from southern France. This population was the most distant geographically from all the others and among the most recent introductions reported in France. In addition, in northern France, AFLP loci revealed a significant river basin effect, despite a common pathway of introduction. This result suggests a shift in local population dynamics, perhaps due to stochastic recruitment, and underlines the importance of local dispersal (e.g. via planktonic larvae) compared to overland transport in shaping the population structure of this naturalized freshwater mollusk.