Once upon a time in Mexico: Holocene phylogeography of the spotted bat (Euderma maculatum)

Holocene-era range expansions are relevant to understanding how a species might respond to the warming and drying climates of today. The harsh conditions of North American deserts have phylogenetically structured desert bat communities but differences in flight capabilities are expected to affect their ability to compete, locate, and use habitat in the face of modern climate change. A highly vagile but data-deficient bat species, the spotted bat (Euderma maculatum) is thought to have expanded its range from central Mexico to western Canada during the Holocene. With specimens spanning this latitudinal extent, we coupled phylogeography (mtDNA) with ecological niche modeling (ENM) to investigate the Holocene biogeography from the rear to leading edges. The ENM and phylogeny supported a Holocene range expansion from Mexico with increased expansion throughout the intermountain west within the last 6 kya. Long-term isolation at the southern-most margin of the range suggests one or more populations were left behind as climate space contracted and are currently of unknown status. The species appears historically suited to track shifts in climate space but differences in flight behaviors between leading edge and core-range lineages suggest that range expansions could be influenced by differences in habitat quality or climate (e.g., drought). Although its vagility could facilitate the tracking of environmental change and thereby extinction avoidance, anthropogenic pressures at the core range could still threaten the ability for beneficial alleles to expand into the leading edge.