Endogean habits drove cryptic diversification in Appalachian Lathrobium Gravenhorst (Coleoptera, Staphylinidae)

The southern Appalachian Mountains are a biodiverse region with high levels of endemism. Shared biogeographic patterns among co-distributed, but independent taxa might illuminate common drivers of Appalachian endemism. Lathrobium is a Holarctic genus with 38 species described form North America, six of which are flightless and endemic to the high Appalachians. We use an integrative morphological and multi-locus molecular dataset to study phylogenetic and biogeographical relationships of Appalachian Lathrobium and test subgeneric hypotheses. A phylogeny based on 176 samples from 67 taxa supported three independent arrivals in the Appalachian Mountains. Divergence times estimated in BEAST2 were concurrent for all three lineages and fell between the Miocene or early Pliocene (16.4 - 4.6 Ma). Speciation within Appalachians occurred during the Pleistocene (2.3 - 0.1 Ma). Monophyly of existing subgenera was supported except for Abletobium Casey. Abletobium is placed in synonymy with Glyptomerus Müller. Our results reveal the importance of cold-climate refugia within the Appalachian Mountains for the persistence and in-situ diversification of endemic endogean taxa. We hypothesize that the xeric climate of the Miocene drove Lathrobium lineages into the mountains and subsequent isolation in mountaintop refugia during warm Pleistocene interglacials led to speciation.