Molecular phylogeny and diversification of the “Haenydra” lineage (Hydraenidae, genus Hydraena), a north-Mediterranean endemic-rich group of rheophilic Coleoptera

Abstract

Hydraena is the largest genus within the water beetle family Hydraenidae, with ca. 1000 species distributed worldwide. Within this large genus some monophyletic groups of species are recognised, among them the “Haenydra” lineage, including ca. 90 species distributed in the western Palaearctic from the Iberian peninsula to Iran. Species of “Haenydra” have often very restricted distributions, and are typical of clean small rivers and streams. We obtained ca. 2.5 Kb of mitochondrial and nuclear protein-code and ribosomal markers of 101 specimens of 69 species of “Haenydra”, and used Bayesian and Maximum Likelihood phylogenetic methods to reconstruct their phylogeny and diversification history. We found a derived phylogenetic position of the “Haenydra” lineage within the genus Hydraena, as sister to the species of the Hydraenabisulcata group.

Within “Haenydra” three main lineages were recognised, with poorly resolved relationships among them: the Hydraena iberica, Hydraena gracilis and Hydraena dentipes lineages, the former restricted to the Iberian peninsula but the latter two distributed through the whole north-Mediterranean area. A Bayesian relaxed molecular clock approach using a combined mitochondrial rate of 2% divergence per MY estimated the origin of “Haenydra” in the Tortonian, ca. 8 Mya, and the main diversification and the origin of most extant species in the Pliocene and Pleistocene. We did not found evidence of a phylogenetic connection between the western and eastern species that could be traced to the Messinian salinity crisis, with dispersal only at small geographical scales (e.g. the colonisation of Corsica and Sardinia from NW Italy and SW France). The H. gracilis and H. iberica lineages were estimated to have diversified under a pure birth model with a speciation rate of 0.64 and 0.23 species/MY respectively, while the H. dentipes lineage was estimated to have a decreasing diversification rate with time, with an average rate of 0.29 sp/MY.