Hybridisation and introgression in the Scottish wildcat

: implications for conservation

Abstract

Hybridisation is an important driver of evolutionary change. Anthropogenic hybridisation, however, (i.e., hybridisation mediated by human activity, for example, through habitat disturbance, introduction of non-native species, or climate change), is considered a threat to wild populations. An important example is the Scottish wildcat, Felis silvestris, which can hybridise with the domestic cat, Felis catus, to produce fertile offspring. Scottish wildcats are the most endangered carnivore species in the UK; this population is considered critically endangered and at serious risk of extinction, as a direct result of hybridisation, in the near future. An overview of the current status of wildcats in Scotland was obtained using a representative sample of 108 individuals from wildcat and domestic cat populations. Hybridisation levels were assessed using 6,546 unlinked SNP markers, highlighting the ‘hybrid swarm’ observed in the wild, i.e., a genetic continuum between the two parent species. Using this information, a subset of 45 individuals from across the hybrid swarm were selected for whole genome resequencing. Additional reference individuals were included in the dataset, specifically, seven samples from mainland populations of European wildcats and 17 domestic cats from a global distribution. Low-coverage data were obtained from historic specimens from early-20th century Scotland. Multiple approaches were taken to model hybridisation and introgression in the Scottish wildcat population, using both the unlinked SNP dataset, and whole genome sequence data. Firstly, a demographic model for wildcats was developed within an approximate Bayesian computational framework. A second approach applied haplotype-based methods to identify local ancestry (wildcat or domestic) across the genome. Results presented here support recent onset of wildcat hybridisation, probably within the last 70 years, and accelerating during the latter part of the 20th century, rapidly generating the ‘hybrid swarm’ structure observed in Scotland today. An improved understanding of past hybridisation dynamics is important for conservation management of this species in the face on continuing gene-flow from domestic cats, in Britain, but also across the species range.

Date of Award	25 Jan 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mark A Beaumont (Supervisor), Daniel John Lawson (Supervisor), Helen Senn (Supervisor), Michael W Bruford (Supervisor) & Andrew Kitchener (Supervisor)