Pii: S0006-3207(98)00067-6

Ferrets (Mustela furo) were domesticated from polecats (M. putorius, M. eversmannii) over 2000 years ago. Following their introduction to Britain, they escaped and hybridized with native European polecats (M. putorius). Native polecats declined to the point of near extinction prior to World War I, but have recently begun to expand from a Welsh refugium. Concern has arisen as to the extent of polecat/ferret introgression, and in particular, whether the expanding population is of mainly hybrid origin. Therefore, mitochondrial DNA sequencing was used to investigate polecat genetic diversity in Britain. Two geographically distinct lineages were found, where one may be ancestral to the British polecat, and the other to the domestic ferret. The ancestral distribution of each lineage, or assortative mating is sucient to explain the observed pattern. A further comparison between the distribution of the polecat phenotype and mitochondrial haplotype implies that the current population expansion may be mediated by dispersing male polecats hybridizing with female feral ferrets. However, the wild source of the ferret remains obscure. Relatively recent speciation from European mink (M. lutreola) and black-footed ferrets (M. nigripes), and/or the e€ects of hybridization result in an unresolved molecular phylogeny. # 1998 Elsevier Science Ltd. All rights reserved.