Investigating the Sicilian-Maghrebian biogeographic pattern in blister beetles (Coleoptera, Meloidae).

Several animal and plant species show a West Mediterranean distribution restricted to Maghreb and Sicily. According to geological evidences, these lands became separated after the opening of the straits of Gibraltar at the beginning of Pliocene (5.33 million years ago). During Pleistocene glaciations, apparently, no land connections occurred between Sicily and Tunisian coasts, even if these lands were greatly approached. Therefore, the presence of species with a fragmented distribution at both shores of the Sicilian channel stimulated two zoogeographic hypotheses: (a) a pre-Pliocene origin of these species, whose range was subsequently fragmented by a vicariance event at the beginning of Pliocene (which implies a quite old species age); (b) Pleistocene dispersal events, during glacial stages, across the Sicilian channel. In order to test these hypotheses, we performed molecular analysis in two blister beetle species (subfamily Meloinae) having a Sicilian-Maghrebian distribution, but belonging to distinct phylogenetic lineages (BOLOGNA, 1991; BOLOGNA and PINTO, 2002): Mylabris schreibersi Reiche, 1866 (tribe Mylabrini), referred to a Palaearctic, widely distributed and speciose genus, and Cabalia segetum (Fabricius, 1792) (tribe Lyttini) belonging to a small Afrotropical genus distributed in eastern Africa, SW Arabian peninsula and Sahara, with the single C. segetum exclusive of Maghreb and Sicily. We sequenced one mitochondrial (COI) and three nuclear (CAD, Wingless, RpS9b) gene fragments in 9 Sicilian and 6-8 Maghrebian (from Morocco and Tunisia) populations of both species. Preliminary results (mainly based on CAD, the most informative gene) show that both species represent cohesive genetic units with a shallow divergence between Maghrebian and Sicilian populations supporting a Pleistocene dispersal scenario. North-African populations show higher genetic variability than Sicilian populations, suggesting an older history of these species in the Maghreb. Additional data and statistical analyses will allow to better understand the phylogeography of M. schreibersi and C. segetum, to estimate timing of population divergence, as well as to infer colonization routes between Maghreb and Sicily.