Phylogenomics and Biogeography of North American Trechine Cave Beetles (Coleoptera: Carabidae)

Abstract

Cave trechines beetles (Coleoptera: Carabidae: Trechini) are members of cave communities globally and important models for understanding the colonization of caves, adaptation to cave life, and the diversification of cave-adapted lineages. In eastern North America, cave trechines are the most species-rich group of terrestrial troglobionts, comprised of over 150 taxa in six genera with no extant surface members. Previous studies have hypothesized the climate change during the Pleistocene was a major driver of cave colonization and diversification in this and other temperate terrestrial cave fauna. However, our time-calibrated molecular phylogeny resulting from the analysis of 16,794 base pairs (bp) from 68 UCE loci for 45 species of the clade supports an alternative hypothesis whereby cave colonization of the surface ancestor of eastern North American cave trechines likely began in the middle Miocene in the Appalachians Ridge and Valley (APP) and dispersed into the Interior Low Plateau (ILP) in an east to west manner around 11.5 Mya. The APP served as a cradle for diversification and also as a bridge linking the southern Appalachians and Interior Low Plateau enabling the dispersal and subsequent diversification of these cave beetles. Major clades in our time-calibrated phylogeny attained their present-day geographic distributions by the early Miocene followed by multiple additional episodes of cave colonization and diversification occurring throughout the Pliocene and Pleistocene. The genera Neaphanops, Darlingtonea, Nelsonites, and Ameroduvalius were nested within specious genus Pseudanopthalmus supporting the hypothesis that these genera are derived Pseudanophtlamus. Moreover, while several morphologically-derived species groups of Pseudanopthalmus were recovered as monophyletic, others were not warranting future taxonomic and systematic research. The molecular systematics and biogeography of these unique cave beetles offer a model for other comparative evolutionary and ecological studies of troglobionts to further our understanding of factors driving speciation and biogeographic patterns.