Parallel habitat-driven differences in the phylogeographical structure of two independent lineages of Mediterranean saline water beetles

It has been hypothesized that species living in small lentic water bodies, because of the short-term geological persistence of their habitat, should show higher dispersal ability, with increased gene flow among populations and a less pronounced phylogeographical structure. Conversely, lotic species, living in more geologically stable habitats, should show reduced dispersal and an increased phylogeographical structure at the same geographical scales. In this work we tested the influence of habitat type in two groups of aquatic Coleoptera (Nebrioporus ceresyi and Ochthebius notabilis groups, families Dytiscidae and Hydraenidae respectively), each of them with closely related species typical of lotic and lentic saline Western Mediterranean water bodies. We used mitochondrial cox1 sequence data of 453 specimens of 77 populations through the range of nine species to compare a lotic vs. a lentic lineage in each of the two groups. Despite the differences in biology (predators vs. detritivorous) and evolutionary history, in both lotic lineages there was a higher proportion of nucleotide diversity among than within groups of populations, and a faster rate of accumulation of haplotype diversity (as measured by rarefaction curves) than in the lentic lineages. Similarly, lotic lineages had a higher absolute phylogenetic diversity, more remarkable considering their smaller absolute geographical ranges. By comparing closely related species, we were able to show the effect of contrasting habitat preferences in two different groups, in agreement with predictions derived from habitat stability.