Investigating genetic introgression from farmed red foxes into the wild population in Newfoundland, Canada

Fur-animal farms can affect the genetic constitution of wild conspecifics through escape and subsequent interbreeding. We studied this problem in red foxes (Vulpes vulpes) on the Canadian island of Newfoundland, where a large commercial fox farm (the only large farm on the island) has operated adjacent to the native wild red fox population for > 30 years. To test for gene flow from these fur-farm foxes into the wild population, we compared mitochondrial DNA (mtDNA) sequences and nuclear microsatellite genotypes (21 loci) of 93 individuals from the fox farm to those of 79 modern wild foxes sampled from across the island. For reference, we also included 12 historical museum specimens of wild eastern Canadian red fox, all of which were sampled before the introduction of fur farming in the region. Many mtDNA haplotypes were shared among contemporary farmed and wild foxes and the historical eastern Canadian samples, as expected based on the eastern Canadian origin of fur-farming. However, only the fur farm additionally contained haplotypes originating from other parts of North America. More significantly, microsatellite markers, which reflect contemporary gene flow, indicated strong differentiation (F (ST) >= 0.14, P < 0.001) between fur-farm and wild foxes (including the historical samples) and little to no gene flow between them. Admixture and principle components analyses similarly supported clear separation of fur-farm and wild red foxes. Together, these findings indicate that the presence of a large red fox fur farm had little, if any, effect on the genetic constitution of the native wild population in Newfoundland. Tight biosecurity (lack of escapees) or failure of captive-reared foxes to establish in the presence of native wild foxes could explain these findings.