INFLUENCE OF GEOLOGICAL BARRIERS ON THE PHYLOGEOGRAPHY AND DISPERSAL OF CAVE-ADAPTED SCOTERPES MILLIPEDES (CHORDEUMATIDA: TRICHOPETALIDAE) IN THE INTERIOR LOW PLATEAU AND APPALACHIANS KARST REGIONS

Caves and associated subterranean habitats represent some of the most unforgiving and challenging environments. However, an amazing array of organisms around the globe have colonized and adapted to living under extreme environmental constraints, including the complete lack of light. Over the last 20 years, the use of molecular approaches in biogeographical studies of subterranean fauna has provided new perspectives into species distributional patterns, cryptic diversity, colonization history, modes of speciation, and the potential influence of hydrological and geological barriers. However, such studies have been limited primarily to cavefishes, salamanders, crayfishes, and spiders in North America. From Scoterpes millipedes, a genus of 15 cave-obligate species endemic to the Interior Low Plateau and Appalachians karst regions of the eastern United States, we examine phylogenetic relationships and the influence of geological barriers on dispersal and gene flow based on mitochondrial and nuclear data. Two hundred specimens from over 120 caves were examined according to their distribution in either region. The Interior Low Plateau has relatively few geological barriers in the horizontal-bedded strata compared to the more frequent barriers occurring in the karst of the Ridge and Valley in the Appalachians. The heavily folded and faulted strata effectively form “karst islands.” Consequently, the current distribution of Scoterpes species can be explained by a combination of both dispersal and vicariance events, and the discovery of cryptic genetic lineages suggests that current levels of species diversity are underestimated.