Early Pliocene range expansion of a clade of subterranean Pyrenean beetles
Correspondence: Ignacio Ribera, Institute of Evolutionary Biology (IBE), Passeig Maritim de la Barceloneta, 37–49, 08003, Barcelona, Spain.
To investigate the possibility of range expansion and diversification within the subterranean environment in a genus of troglobiont beetles of the family Leiodidae (Troglocharinus), which have a disjunct distribution between the Pyrenees and the Catalonian coast.
North-eastern Iberian Peninsula.
We sequenced 4 kb of five mitochondrial and two nuclear genes of 50 specimens of 12 of the 18 species of Troglocharinus, plus several outgroups. We reconstructed a phylogeny using Bayesian inference and maximum likelihood, estimated divergence times using Bayesian probabilities and an a priori evolutionary rate, compared the diversification of the main clades within the genus, and reconstructed their ancestral distribution using maximum likelihood.
We found strong support for the monophyly of Troglocharinus and the clades in each of the geographical areas, which diverged in the early Pliocene. The coastal clade was further divided into geographically well-defined lineages, separated by Quaternary deposits. The origin of the coastal clade was a single colonization in the early Pliocene from the central Pyrenees. The diversification of the Pyrenean clade followed a constant rate, while the diversification rate of the coastal clade significantly decreased through the Plio-Pleistocene transition.
Troglocharinus expanded its range from its ancestral area in the central Pyrenees to the coast of Catalonia and subsequently diversified, probably within the subterranean environment. Our favoured scenario is a stepping-stone migration, with possibly short-distance dispersals through the surface, along the eastern margin of the north-eastern Ebro basin. The range expansion took place in a narrow temporal window with favourable conditions between the early Pliocene and the onset of the Mediterranean climate by the mid-Pliocene. Surface dispersal was probably severely limited afterwards, as shown by the fragmentation of the coastal lineage.