Data from: Phylogeographic history and future outlook of a flightless, saproxylic beetle within high-elevation southern Appalachian forests Clayton R. Traylor1, Michael S. Caterino2, Michael D. Ulyshen3, Michael L. Ferro2, Joseph V. McHugh1 1University of Georgia, Department of Entomology, Athens, Georgia 30602, USA 2Clemson University, Plant and Environmental Sciences Department, Clemson, South Carolina 29634, USA 3USDA Forest Service, Southern Research Station, Athens, Georgia 30602, USA Abstract Within the never-glaciated southern Appalachian Mountains, today’s high-elevation forest types are fragmented after contracting from continuous distributions during the last glacial maximum (LGM). Species restricted to high-elevation forests show a genetic history of severe to moderate isolation dictated by dispersal ability, despite historic habitat continuity. However, examples of specialist species with known natural histories are scarce. We investigated the phylogeography of Phellopsis obcordata (Kirby) (Coleoptera: Zopheridae), a flightless, saproxylic beetle that, within the southern Appalachians, depends on old-growth forests at high elevations. We specifically sought to understand drivers of gene flow and genetic diversity to inform conservation efforts today and under future climate change scenarios. We used phylogenetic divergence time estimation and population genetic analyses on mitochondrial DNA (COI) to infer phylogeographic history, and modelled its distribution with Maxent at the LGM, today, and under climate change scenarios in 2070. Phylogenetic analyses recovered five geographically distinct clades, four of which were highly supported. The clades diverged in the late Pliocene/early Pleistocene with several examples of secondary contact in the Pleistocene, including across the Asheville Basin. Additionally, no populations were monophyletic, with intra-clade mixing apparent. Population genetic analyses indicate population stability, high genetic diversity, and modern-day isolation. Distribution models suggest widespread suitability in the southern Appalachians and beyond at the LGM, fragmented suitability only in high elevations today, and range-wide reductions in suitability in 2070 based on both moderate and severe climate change scenarios. Our results indicate that expansion events, likely during glacial maxima, have shifted lineages and allowed connectivity of isolated populations within the southern Appalachian Mountains. Various isolating factors may be responsible, but apparently have been bridged occasionally throughout the Pleistocene by this flightless species. Inclusion of both nuclear DNA and increased geographic sampling are necessary for better insight of admixture and clade distributions. Regardless, our results suggest that unique intraspecific diversity may be at risk with a warming climate. Key words: biogeography, deadwood, fungus beetle, glacial refugia, montane spruce-fir forest, old-growth forest