Crossing the Rhine: a potential barrier to wildcat (Felis silvestris silvestris) movement?

The European wildcat (Felis silvestris silvestris) underwent a severe decline across Europe in the early twentieth century. Remaining populations are often very small and isolated, though there are indications that wildcat populations are currently expanding their range. However, linear landscape elements such as rivers and roads are thought to present barriers to dispersal, inhibiting gene flow and, thus, affecting the recolonization process. In this study, we investigated the fine-scale genetic structure of wildcats in the Upper Rhine Valley. We specifically analysed wildcats on both sides of the Rhine River by genotyping 55 individual wildcats, using 20 microsatellite loci. Genetic differentiation was weak and positive spatial autocorrelation was found up to a distance of 10 km (females: 5 km, males: 10 km) indicating substantial gene flow among sampling sites. High levels of gene flow, even across the Rhine River, indicated that the water body itself does not necessarily have a strong barrier effect, which is in contrast to other studies. Our findings could best be explained by the populations’ history, a local extinction east of the River Rhine and a current ongoing population expansion. Our study highlights that potential barriers, such as rivers, may have different effects in different local wildcat populations and that the history of the populations is important to interpret genetic results. As many wildcats still occur in isolated and patchy forest fragments, maintaining connectivity between populations is crucial to ensure their viability in the long term.