UK polecat numbers may be rising due to interbreeding with ferrets

The population of polecats in Britain has recovered over the past century and it may be in part due to interbreeding with feral ferrets

Life 18 August 2022

Mandatory Credit: Photo by Jurgen Christine Sohns/Imagebroker/Shutterstock (4401886a) European Polecat (Mustela putorius), adult, alert, Surrey, England, United Kingdom VARIOUS

Polecats in England are hybrid ferrets

Jurgen Christine Sohns/Imagebroker/Shutterstock

Many wild polecats in Britain are part ferret. The weasel-like mammals have thoroughly interbred with their domesticated relatives as they’ve spread out from a small population in Wales.

European polecats (Mustela putorius) are thought to be the ancestors of ferrets (M. putorius furo), which were domesticated roughly 2000 years ago. Initially widespread in Britain, polecats were persecuted by humans as predators of poultry and game birds, and by 1900, British polecats persisted only in small pockets of Welsh forest.

Declines in gamekeeping after the two world wars, bans of certain traps, and formal protection under the Wildlife & Countryside Act in 1981 have contributed to polecat recovery. Over the last several decades, polecat population have expanded eastward through England, which is home to feral ferret populations. The two animals were known to be interbreeding, but researchers hadn’t determined the extent in detail, says Graham Etherington at the Earlham Institute, UK.


Etherington and his colleagues took DNA samples from 49 different Mustela individuals, including roadkill polecats from Britain and mainland Europe, putative hybrids, and domesticated ferrets. The team analysed and compared the mammals’ genomes.

All the British polecats’ genomes had evidence of interbreeding with ferrets, the degree of which mirrors the polecats’ pattern of geographical expansion across Britain.

“The further away you get from Wales, the more ferret-like they get,” says Etherington.

Even individuals that appeared to be “pure” polecat based on physical features had ferret origins for much of their genome.

The team also looked for genes in the English population of hybrid polecats that were always inherited from ferrets. “Those versions of the genes have been selected for presumably because they give the polecat some sort of advantage,” says Etherington.

Two of these human versions of genes are thought to have roles in cognition and vision in humans, so it’s possible they have similar influence in Mustela. Etherington wonders if such ferret genes augmented hunting ability, became a more prominent feature in ferrets thanks to human breeding, and now are finding a second life in polecats. Determining this would require further research.

Frank Hailer at Cardiff University, UK notes that there could be positives for rare or endangered species that hybridise with close relatives.

“Perhaps such interbreeding helps species survive by giving them access to genetic variation that they don’t have themselves?”, says Hailer, who was not involved with this research.

Etherington and his team also found notable genetic differences between Welsh polecats and their English and mainland cousins, and are currently determining whether the Welsh population could be a distinct species.

Journal reference: Journal of Heredity, DOI: 10.1093/jhered/esac038

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