Extent of introgressive hybridization in the Hermann's tortoise (Testudo hermanni hermanni) from the south of France

The Western subspecies of Hermann's tortoise (Testudo hermanni hermanni: WT) is threatened by habitat loss, fragmentation, wildfires, illegal harvesting, and likely hybridization with Testudo hermanni boettgeri (ET), a subspecies introduced from Eastern Europe. To assess the prevalence of this hybridization, we used microsatellite markers and simulations to investigate the genetic status of 565 individuals of the Var district (France) in contrast to the genetic signature of 121 individuals sampled in the Balkans. The genetic differentiation between WT and ET indicated 18% of tortoises in the Var were hybrids between WT and ET (i.e. F1, F2, and F3). Although hybridization increases the genetic diversity within the genetically impoverished WT population, hybridization could also threaten WT genetic integrity. Identifying and removing all hybridized individuals (especially beyond F1) is logistically unfeasible. Instead, conservation actions should reinforce communication and education, notably towards pet owners, to limit further hybridization. Moreover, accurate genetic identification of captives is essential to programs that involve translocating individuals to fragile populations (e.g. those severely impacted by bush fires). Further studies should assess the extent that WT/ET hybridization is detrimental or beneficial to populations facing rapid global changes in the context of depressed genetic diversity.