Speciation of rock-dwelling snail species: disjunct ranges and mosaic patterns reveal the importance of long-distance dispersal in Chilostoma (Cingulifera) in the European Southern Alps

In order to better understand the origin of the high diversity and endemism in the Southern Alps in Europe, we examined the phylogeny and population structure of the rock-dwelling snail group Chilostoma (Cingulifera) in the Southern Alps. We generated genomic ddRAD data and mitochondrial sequences of 104 Cingulifera specimens from 28 populations and 14 other Ariantinae. Until recently, about 30 Cingulifera taxa were classified as subspecies of a single polytypic species. The phylogenetic and population genetic analyses of the ddRAD data and mitochondrial sequences revealed that Cingulifera is differentiated into three species in the Southern Alps. Each of the three Chilostoma (Cingulifera) species occupies disjunct subareas, which are separated by areas occupied by other Chilostoma taxa. Neighbouring populations of different species show no or little admixture. Tests indicating that the differentiation of the three Cingulifera taxa cannot be explained by isolation by distance corroborated their species status. The disjunct differentiation patterns demonstrate the importance of stochastic events like passive long-distance dispersal, extinction and priority effects for the evolution of the population structure and speciation in these snails.