Background: The Alpine region harbours one of the most diverse subterranean faunas in the world, with many species showing extreme morphological modifications. The ground beetles of tribe Trechini (Coleoptera, Carabidae) are among the best studied and widespread groups with abundance of troglobionts, but their origin and evolution is largely unknown. Results: We sequenced 3.4 Kb of mitochondrial (cox1, rrnL, trnL, nad1) and nuclear (SSU, LSU) genes of 207 specimens of 173 mostly Alpine species, including examples of all subterranean genera but two plus a representation of epigean taxa. We applied Bayesian methods and maximum likelihood to reconstruct the topology and to estimate divergence times using a priori rates obtained for a related ground beetle genus. We found three main clades of late Eocene-early Oligocene origin: (1) the genus Doderotrechus and relatives; (2) the genus Trechus sensu lato, with most anisotopic subterranean genera, including the Pyrenean lineage and taxa from the Dinaric Alps; and (3) the genus Duvalius sensu lato, diversifying during the late Miocene and including all subterranean isotopic taxa. Most of the subterranean genera had an independent origin and were related to epigean taxa of the same geographical area, but there were three large monophyletic clades of exclusively subterranean species: the Pyrenean lineage, a lineage including subterranean taxa from the eastern Alps and the Dinarides, and the genus Anophthalmus from the northeastern Alps. Many lineages have developed similar phenotypes independently, showing extensive morphological convergence or parallelism. Conclusions: The Alpine Trechini do not form a homogeneous fauna, in contrast with the Pyrenees, and show a complex scenario of multiple colonisations of the subterranean environment at different geological periods and through different processes. Examples go from populations of an epigean widespread species going underground with little morphological modifications to ancient, geographically widespread lineages of exclusively subterranean species likely to have diversified once fully adapted to the subterranean environment.

This work has been partly funded by an Alexander von Humboldt Foundation grant and German Research Foundation projects (BA2152/14-1 and FA 1042/1-1), the Italian PRIN (Research Programmes of National Interest, University of Sassari) “The endemism in Italy” and the R.A.S. Project CRP-60215 (2012) “Conservation and valorisation of the Sardinian caves: biodiversity and social, cultural and economic rules” to AC, and project CGL2010-15755 from the Spanish government to IR