Biogeography and radiation of the land snail genus Xerocrassa (Geomitridae) in the Balearic Islands

Aim Our aim was to assess the evolutionary history of the land snail genus Xerocrassa on the Balearic Islands with a molecular phylogeny. We investigated how the main palaeogeographical events and climate changes which occurred in the Western Mediterranean basin influenced the current diversity and distribution of the genus within the archipelago. Location The Balearic Islands, Western Mediterranean. Methods A dataset of 2540-bp DNA sequences was generated from one nuclear and two mitochondrial gene fragments obtained from 170 specimens representing 112 populations. Applying maximum likelihood and Bayesian phylogenetic methods and a Bayesian molecular clock, we examined the evolutionary history of the genus Xerocrassa. We also used genetic-based species delimitation models to clarify the taxonomy of the genus in the archipelago. Results We provide the first molecular phylogeny of the endemic Xerocrassa of the Balearic Islands. The monophyly of several currently recognized species was not supported. The genus colonized the archipelago in a single event during the Messinian salinity crisis (5.96-5.33 Ma) from the eastern part of the Iberian Peninsula. The hypothesis of a relatively recent origin for the evolutionary diversification within the group was supported by molecular clock analyses. Allopatric speciation occurred after the isolation of the Pityusic and Gymnesic island systems. Moreover, most of the extant species are the result of within-island speciation events. Main conclusions Historical biogeographical reconstruction strongly supports the hypothesis of Messinian salinity crisis as the colonization period of the Balearic Islands for Xerocrassa. Major climate changes experienced in the Western Mediterranean basin during the Plio-Pleistocene influenced the within-island speciation processes postulated for Xerocrassa. The high morphological diversity in the genus represents 11 species and a strong phylogeographical structure within the main islands.