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

To better understand the origin of the high diversity and endemism in the Southern Alps of Europe, we inves-tigated 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 sub-species of a single polytypic species. The phylogenetic and population genetic analyses of the ddRAD data and mitochondrial sequences revealed that Cingulifera in the Southern Alps is differentiated into three species. Each of the three Chilostoma (Cingulifera) species occupies disjunct sub-areas, which are separated by areas occupied by other Chilostoma taxa. Neighbouring populations of different species show little or no admixture. Tests indicating that the genetic differentiation of the three Cingulifera taxa cannot be explained by isolation by dis-tance confirmed their species status. The disjunct range patterns demonstrate the importance of stochastic events such as passive long-distance dispersal for the evolution of population structure and speciation in these snails, and of priority effects and ecological competition as important factors influencing species distributions.

Automated summary

By studying the rock-dwelling snail group Cingulifera in the Southern Alps, we discovered high species diversity and endemism. Genomic analysis of 104 Cingulifera specimens from 28 populations and 14 other Ariantinae revealed that there are three distinct species in the region. These species occupy separate sub-areas and show little admixture with neighboring populations of different species. This study highlights the importance of stochastic events, priority effects, and ecological competition in shaping population structure and speciation in these snails.