A molecular phylogeny shows the single origin of the Pyrenean subterranean Trechini ground beetles (Coleoptera: Carabidae)

Trechini ground beetles include some of the most spectacular radiations of cave and endogean Coleoptera, but the origin of the subterranean taxa and their typical morphological adaptations (loss of eyes and wings, depigmentation, elongation of body and appendages) have never been studied in a formal phylogenetic framework. We provide here a molecular phylogeny of the Pyrenean subterranean Trechini based on a combination of mitochondrial (cox1, cyb, rrnL, tRNA-Leu, nad1) and nuclear (SSU, LSU) markers of 102 specimens of 90 species. We found all Pyrenean highly modified subterranean taxa to be monophyletic, to the exclusion of all epigean and all subterranean species from other geographical areas (Cantabrian and Iberian mountains, Alps). Within the Pyrenean subterranean clade the three genera (Geotrechus, Aphaenops and Hydraphaenops) were polyphyletic, indicating multiple origins of their special adaptations to different ways of life (endogean, troglobitic or living in deep fissures). Diversification followed a geographical pattern, with two main clades in the western and central-eastern Pyrenees respectively, and several smaller lineages of more restricted range. Based on a Bayesian relaxed-clock approach, and using as an approximation a standard mitochondrial mutation rate of 2.3% MY, we estimate the origin of the subterranean clade at ca. 10 MY. Cladogenetic events in the Pliocene and Pleistocene were almost exclusively within the same geographical area and involving species of the same morphological type.