Monitoring introgression in European wildcats in the Swiss Jura

Introgression is an important evolutionary force, which can lead to adaptation and speciation on one hand, but on the other hand also to genetic extinction. It is in the latter sense that introgression is a major conservation concern, especially when domestic species reproduce with their rare wild relatives. Hence, monitoring introgression in natural populations subject to hybridization is crucial to elucidate the threat represented by introgression. Here, we monitored introgression between wildcats ( Felis silvestris silvestris ) and domestic cats ( Felis silvestris catus ) in a wildcat population in the Swiss Jura Mountains using systematically and non-invasively collected hair samples. We found 21 % admixed individuals based on 68 diagnostic nuclear SNP-markers, corresponding to a migration rate from domestic cats to wildcats of 0.02 migrants per generation. In contrast, gene flow from wildcats into domestic cats was negligible. Haphazard sampling of the same wildcat population, mostly via road kills, led to similar results. Hybridization occurred between wildcat male and domestic cat female and vice versa and, based on the occurrence of backcrosses, both female and male F1-hybrids seem viable and fertile. The observed hybridization pattern may indicate an expanding wildcat population with introgression as a byproduct of this expansion but alternative explanations cannot be excluded with the current data.