The Eastern Fox Squirrel (Sciurus niger) exhibits minimal patterns of phylogeography across native and introduced sites.

Introduced species are one of the leading causes of declining global biodiversity and result in many billions of dollars of losses to the bioeconomy worldwide. Introduced species have become increasingly common due to globalization and climate change, and population genetics is a useful tool for the management of such species. The Eastern Fox Squirrel (Sciurus niger) is a highly successful invader that was introduced to many states in western North America throughout the 20th century. We used low-pass whole genome sequencing to evaluate phylogeographic structure across native and introduced ranges of this species and identify the putative number and geographic sources of introductions in California and Utah. We found minimal patterns of phylogeographic structure, consistent with recent range and population expansion since the Last Glacial Maximum. Additionally, we found evidence for multiple mitochondrial haplotypes in California and only 1 haplotype in Utah, which suggests that fox squirrels in California were sourced from multiple introduction events while those in Utah were likely sourced from a single event. Genomic resources generated in this study will be useful for future conservation efforts in this species and will assist with the ongoing management of its introductions across western North America.