Genetic structure and dynamics of a small introduced population: the pikeperch, Sander lucioperca, in the Rhône delta.

Genetic data on introduced populations may help us to understand how these species succeed in colonising new territories. The pikeperch is a predatory fish widely introduced in Europe and has at times been considered as an invasive species. However, little is known about the genetics of both native and introduced populations. In the present study, we surveyed an introduced pikeperch population from the Rhône River delta, a habitat that has been highly modified for agricultural purposes. Using six microsatellites, we genotyped 93 individuals distributed among four hydraulically connected water bodies: the Rhône River, an irrigation canal, a drainage canal and a brackish lagoon. Population isolation were revealed by significant genetic distances and bottleneck highlighted by population monitoring. However, values of allelic richness and unbiased expected heterozygosity observed in these populations were similar, or even higher, compare to 18 native populations from the Baltic Sea drainage. It may be explained by multiple introductions in the Rhône drainage but also by demographic strategy that would have facilitated population persistence in this fragmented habitat. Similarly, heterozygote deficits (revealed by F(IS) values) have been detected, but were also found in native populations suggesting that mating among relatives could also result from a mating behavior of the species, maybe reinforce here by the reduced carrying capacity of the artificial canals and their respective isolation. Despite harsh environmental conditions and suspected inbreeding, the pikeperch has successfully maintained viable populations in the Rhône delta. Our study suggests that one of the factors in this invasive success, apart from its ecology, could be the maintenance of a good level of genetic diversity in introduced pikeperch populations. This genetic diversity probably stem from both its popularity as game fish and food resource which led to numerous stocking and an increasing propagule pressure and the reproductive strategy of the species.