The geography of speciation in narrow endemics of the “Haenydra” lineage (Coleoptera, Hydraenidae, Hydraena)

Aim We compare different scenarios for the origin of the endemic western Mediterranean species of aquatic Coleoptera of the “Haenydra” lineage (Hydraenidae, Hydraena) through contrasting predictions of the relationship between their phylogenetic and geographic distance. We test whether species originated 1) through successive periods of dispersal and speciation, or through fragmentation of the range by 2) random vicariance or 3) geographical isolation due to a general rarefaction of the population density. Location Europe. Methods We build a phylogeny using 3Kb of three mitochondrial and two nuclear gene fragments of ca. 50% of the known species of “Haenydra”, including all the western Mediterranean taxa. We estimated divergence times with a molecular clock and compiled the distribution of the species and their geographical centroids. We tested the relationship between geographical and phylogenetic distance using bivariate plots, mantel tests and the comparison of the observed phylogeny with the one minimising geographical distances between species, as measured with an Euclidean Minimum Spanning Tree (EMST). Results The monophyly of “Haenydra” was strongly supported, although its phylogenetic placement within Hydraena was not resolved. “Haenydra” was estimated to be of Tortonian origin, with most of the current species originating during the Pleistocene. Four well-sampled lineages including most of the Iberian endemics were chosen for the detailed geographical analyses. In two of them (H. tatii and H. emarginata clades) there was a significant association between geographical and phylogenetic distance, and the reconstructed phylogeny was identical to that obtained through the EMST, demonstrating a strong non-randomness of the geographical distribution of the species. In the other two (H. iberica and H. bitruncata clades) there was no association between geographical and phylogenetic distance, and the observed phylogeny was not the one minimising geographical distances. In one of the clades this lack of association seems to be due to the secondary recent expansion of one of the species (H. iberica), erasing the geographical signal of their distributions. Main conclusions We show that it is possible to obtain strong evidence of stasis of the geographical ranges of narrow endemic species through the study of their phylogenetic relationships and their current distributions. In at least two of the studied clades current species seem to have originated through the fragmentation of a more widely distributed species, without further range movements. This process of range expansion and fragmentation seems to have occurred repeatedly within the “Haenydra” lineage, contributing to the accumulation of narrow endemics in Mediterranean Pleistocene refugia.