Is there a northern dispersal corridor between Southeast and Central Asia? Evidence from the freshwater snail Radix plicatula

The freshwater fauna of Central Asia is largely composed of widespread Eurasian taxa and shares little overlap with the highly endemic assemblages of Southeast Asia. Here, we report the first record of the Southeast Asian Pond snail Radix plicatula (W. H. Benson, 1842) in Central Asia (northern Tien Shan, Kazakhstan), extending its known range by approximately 2,200 km. To assess the origin of this population, we combined morphological data, genetic analysis, and species distribution modelling. Phylogenetic analyses place the Tien Shan specimens within the main Radix plicatula lineage, while haplotype data reveal unexpectedly high genetic diversity within a geographically restricted area. This pattern is inconsistent with a recent anthropogenic introduction and instead suggests long-term persistence. Species distribution models produced contrasting results depending on background selection. Models with unrestricted background predicted a range largely confined to Southeast Asia, whereas models with spatially constrained background and land-cover variables indicated substantially broader suitability, including Central Asia. This discrepancy suggests that the present-day distribution of Radix plicatula is not solely determined by climate. Palaeoclimatic projections indicate that suitable habitats were more widespread in the past, forming a belt north of major Asian mountain systems. Together with molecular evidence, this suggests a scenario of Pleistocene dispersal between Southeast and Central Asia.