109 Population genomics of the eastern fox squirrel (Sciurus niger) across native and introduced ranges

Faculty Mentor: Dylan Klure (School of Biological Sciences, University of Utah)

Understanding the origins of invasive species is critical to their management. The fox squirrel (Sciurus niger) is a highly successful invasive species in North America that was introduced to many western states throughout the 20th century. Fox squirrels were first recorded in Utah in 2011 and have quickly become dominant in urban environments; however, the origin of Utah’s fox squirrels is unknown. Based on morphological characteristics, we hypothesize that Utah’s fox squirrel population was likely introduced from Texas. We generated preliminary sequence data from the mitochondrial cytochrome B (mtCytB) gene for 16 individuals sampled in Utah and found there was only a single mtCytB haplotype present in this population, indicative of their recent introduction and high levels of inbreeding. We determined that sequence data from this single gene was inadequate to identify the putative origins of introduced S. niger populations in the western United States; therefore, we employed population genomics to obtain better sequence resolution for resolving the population structure of this species. We performed whole genome sequencing on 32 S. niger individuals from across North America, covering both native and introduced sites from 10 states. Despite low levels of genetic differentiation across most individuals, we found strong evidence that there has likely been only a single introduction of fox squirrels into Utah, whereas California’s population is likely the result of multiple independent introductions. Utah’s fox squirrel population is most genetically similar to individuals sampled from nearby geographic localities, suggesting the source of this introduction is likely from a neighboring state rather than Texas as initially hypothesized. The limited population structure within this species across both its native and introduced ranges is consistent with recent rapid population expansion since the Last Glacial Maximum (~20 KYA). These findings provide additional insight into both the historic and current range expansions of this species which is critical for improving our understanding of the invasion dynamics of fox squirrels. In addition, the sequence data for this study will be made publicly available to aid future studies focused on resolving the phylogeography of this species and identifying the key adaptation that enable them to be such successful invaders.