Abstract
BackgroundThe 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.ResultsWe 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.ConclusionsThe 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.
Highlights
The Alpine region harbours one of the most diverse subterranean faunas in the world, with many species showing extreme morphological modifications
Phylogenetic analysis The estimated optimal evolutionary model was GTR + I + G for the three mitochondrial gene partitions and the nuclear small ribosomal unit (SSU), and GTR + G for the nuclear large ribosomal unit (LSU)
Clade 1 (Figures 3a-c and 4) included most of the anisotopic species: the Pyrenean hypogean lineage, the genus Epaphius and relatives (Blemus and some species of Trechus, clade 1.2) and a large group including most species of the genus Trechus plus a number of subterranean genera nested within it
Summary
The Alpine region harbours one of the most diverse subterranean faunas in the world, with many species showing extreme morphological modifications. Faille et al [13] included other highly modified western Mediterranean cave Trechini considered by some authors to be related to the Pyrenean fauna (i.e. to be members of the “phyletic lineage” of Aphaenops in the sense of Jeannel [2]), such as the Iberian Apoduvalius and Paraphaenops, Speotrechus from southeastern France, or the Sardinian Sardaphaenops. All these species were found to be not related to the Pyrenean fauna but to other lineages in the same geographical areas, showing again a strong morphological convergence among them [13]. In that study the basal relationships among the main lineages of the western Mediterranean fauna of Trechini could not be established, likely due to the lack of representation of more eastern lineages
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