The role of Anatolia in the origin of the Caucasus biodiversity hotspot illustrated by land snails in the genus Oxychilus

Abstract

Several taxa that are distributed in the Caucasus and/or the adjacent Pontic Mountains also have representatives in the East Mediterranean region. These disjunctions could have been caused by long-distance dispersal or be the result of extinctions in Central Anatolia caused by the aridification of the Anatolian Plateau during the Pliocene. We studied the Longiphallus-Hiramia group of Oxychilus as an example showing such distribution patterns. Phylogenetic analyses of the Oxychilus species previously classified in Longiphallus, Hiramia and related subgenera resulted in a new delimitation of these taxa and the recognition of Anatoloxychilus Neiber, Walther & Hausdorf n. subgen. as an additional clade. Based on phylogenetic and population genetic analyses, O. reticulatus from Mingrelia is revalidated and the populations from the Pontic Mountains previously identified with O. mingrelicus koutaisanus are recognised as a distinct species. Three species pairs of the Longiphallus-Hiramia group with deep splits predating the aridification of the Anatolian Plateau during the Pliocene show disjunctions between the Caucasus/Pontic region and the Mediterranean. The majority of taxa with such a distribution pattern probably had more continuous distributions before the aridification started. The relationships between the Hiramia species from the Caucasus, the Pontic Mountains and the East Mediterranean highlight the importance of the Anatolian land as a source area for the colonisation of the Caucasus region. The dating of the divergences of the Caucasian Hiramia species in the middle to late Miocene indicated that they colonised the Caucasus when it was still an island in the Paratethys Sea and that their divergence was triggered by the orogenesis of the Greater Caucasus. A common pattern within the Caucasus region, also found in Hiramia, is the separation of taxa in the north-western Greater Caucasus from taxa inhabiting the southern slopes of the central Greater Caucasus.