Invasive genetic rescue: dispersal following repeated culling reinforces the genetic diversity of an invasive mammal

Abstract

Since its introduction from the United States in 1876 the invasive North American Eastern grey squirrel (Sciurus carolinensis) has contributed to the decline of the native Eurasian red squirrel (Sciurus vulgaris) in Britain. Consequently, grey squirrel populations are often subjected to extensive control efforts in order to reduce local abundance and prevent spread, particularly within habitats containing red squirrels. Grey squirrel removal from the island of Anglesey off the coast of north Wales began in 1998 and was completed in 2013. A parallel successful red squirrel reinforcement translocation project also took place. The narrow seachannel, road and rail bridge connection has meant that the adjacent mainland grey squirrel population has been controlled in subsequent years to reduce the probability of re-invasion.The aim of this study was to assess the overall impact of repeated culling efforts carried out between 2011 and 2020 on the genetic diversity of the grey squirrel population in north Wales to inform future adaptive management plans. Using a combination of mitochondrial DNA (mtDNA) and microsatellite DNA analysis, we found high genetic diversity in both marker types, with six diverse mtDNA haplotypes found and relatively high levels of nuclear genetic diversity, even after repeated culling efforts. Our results suggest that ongoing culling efforts may not adequately reduce genetic diversity to a level where it contributes to a longterm population decline.

Genetic Lag in a Demographically Recovering Carnivore: The Case of the British Pine Marten (Martes martes)

“…one site with 30 animals had a H e of 0.4 and H o of 0.39 and 3.2 alleles (Fraser et al, 2013). The invasive North American grey squirrel in North Wales also had high genetic diversity, with H e and H o averaging 0.56 and 0.35 respectively, and the number of alleles averaging 6.7 (Synnott et al, 2023). Despite regular culling of the species in North Wales, over a 10 year period, the population was not found to have experienced any signi cant decreases in diversity, due to the inward migration of new animals with divergent genetic origins in North America, encompassing a total of six distinct mtDNA haplotypes within a relatively small geographic area.…”