Systematics and evolutionary history of large endemic snails from the Caucasus (Helix buchii and H-goderdziana) (Helicidae)

摘要

Two species of genus Helix Linnaeus, 1758 (Mollusca: Gastropoda: Helicidae) endemic to the Caucasus region are known from Georgia and northeastern Turkey: Helix buchii Dubois de Montpereux, 1839 and the recently-described but disputed Helix goderdziana Mumladze, Tarkhnishvili and Pokryszko, 2008. The latter species is the largest land snail throughout non-tropical Eurasia. We compared shell shapes and genital morphology of the two species. We analyzed mitochondrial COI and nuclear 18S ribosomal RNA and ITS1 gene fragments in 39 specimens of H. buchii and H. goderdziana from ten locations from the entire distribution range of these species, together with 13 specimens of the widespread H. lucorum Linnaeus, 1758 and H. pomatia Linnaeus, 1758. Based on shell morphology alone, most of the individuals of the two species can be discriminated using multivariate approaches. The species have different flagellum/diverticulum ratios, and the foot coloration is a fully diagnostic morphological character. Molecular genetic analysis revealed little variation in 18S+ITS1 fragment, and eleven COI haplotypes. Phylogenetic analyses support reciprocal monophyly of H. buchii and H. goderdziana. The genetic distances significantly correlate with the geographic and morphological distances; correlation of morphological distances with geography is insignificant. The basal lineages of both species are found within two distinct glacial refugia, a result which matches the separation of eastern and western evolutionary lineages of other relicts of the Western Caucasus. The present distribution of H. goderdziana coincides with the expected refugial borders, whereas H. buchii is likely to have extended its geographical range since the last glaciation.