Species delimitation in the genus Bythinella (Mollusca: Caenogastropoda: Rissooidea):: A first attempt combining molecular and morphometrical data

Within the springsnail genus Bythinella, few discontinuous morphological characters allow to unambiguously delineate species-level taxa. Opinions on the alpha-taxonomy of the group are divergent, with some authors recognizing every morphologically distinct local form as a species, while others interpreting such geographical forms as intraspecific variation. Because the value of morphological characters was rarely contrasted with molecular data, such opinions remained untested. In this work, variation between populations was studied through genetics isozymes, phylogeny (DNA), and morphometrics. Eleven populations representing five putative species were sampled from the French Pyrenees, a region where a high number of nominal species are classically recognized. Based on genetic and phylogenetic analyses, the material clusters into three groups, of which one consists of several nominal species. Environmental factors, sexual dimorphism, and genetic factors contribute to the significant morphological variation observed within the genetic groups. Thus, the number of species of Bythinella recognized in the Pyrenees appears probably overestimated, and the characters traditionally used for species delimitation should be re-evaluated.