Abstract
Biological invasions by non-native species pose significant threats to agriculture, ecosystems, human health, and economies. Despite the efforts of management agencies, many populations of invasive species continue to persist and spread, necessitating a deeper understanding of the processes influencing their growth and expansion. We investigated the potential for unwanted genetic rescue to increase the population growth rate and spread of invasive European fallow deer (Dama dama) in south-eastern Australia. Using a single nucleotide polymorphism dataset from over 340 individuals, we assessed genetic diversity, levels of inbreeding, and population structure and connectivity. We found low genetic diversity and heightened inbreeding across most fallow deer surveyed, highlighting potential for inbreeding depression. However, a small number of populations had significantly higher diversity and lower inbreeding. We hypothesize that the high diversity populations stem from farmers importing diverse fallow deer lineages for artificial breeding, with some of those animals (or their progeny) subsequently escaping or being released into the wild. We explored the potential for recently imported genetic variants to spread across populations by examining population connectivity. Finally, to demonstrate the risk of unwanted genetic rescue in fallow deer, we simulated population growth under different scenarios and show that reduced inbreeding is expected to substantially increase population growth rates. Our study highlights the importance of integrating genetic considerations into invasive species control. To enhance deer management in Australia we recommend considering migration patterns in control program design, containing high-diversity populations, and strengthening the containment and biosecurity requirements of farmed and imported deer.
