Evolution, mitochondrial DNA phylogeny and systematic position of the Macaronesian endemic Hydrotarsus Falkenstrom (Coleoptera: Dytiscidae)

Hydrotarsus Falkenstrom (Coleoptera, Dytiscidae) is the only genus of aquatic beetle considered to be endemic to the Atlantic islands of Macaronesia. Its three known species (H. lundbladi Falkenstrom from Madeira, and H. compunctus (Wollaston) and H. pilosus Guignot from the Canary Islands) are revised, and their phylogenetic position studied based on sequences of the 16S rRNA and Cytochrome Oxidase I genes of mitochondrial DNA. Our results clearly indicate that the species of Hydrotarsus fall deep within the genus Hydroporus Clairville, in a clade formed by (in addition to Hydrotarsus) species currently included in the H. fuscipennis, marginatus, nigrita and tessellatus groups, and in consequence a new synonymy is proposed: Hydrotarsus Falkenstrom = Hydroporus Clairville syn.n. The origin of the species of 'Hydrotarsus', based on molecular clock estimations, is late Miocene, relatively recent in the history of the Atlantic islands. They are therefore not palaeoendemics but highly derived, recently evolved elements in the Macaronesian fauna. The estimated ages of divergence among species are much more recent than the emergence of any of the islands on which they are found, suggesting rare long-range dispersal as the mechanism driving the diversification of the lineage. Morphological modifications of the species of 'Hydrotarsus' are discussed, as well as those of other dytiscids from hygropetric habitats.