Karyological Diversification of Trochoidea caroni (Gastropoda, Pulmonata, Geomitridae) Between Sicilian and Non-Sicilian Populations

Trochoidea caroni (Gastropoda, Geomitridae) is a land snail previously found only in Sicily and Capri (Naples), but it has recently been found in other regions of the Italian peninsula. In this study, we performed karyological and molecular analysis on T. caroni from different sites across this regional range. Karyological analysis was performed on specimens from Palermo (Sicily), Capri (Campania), and Terracina (Lazio) using standard staining and NOR-FISH methods; the latter method was also performed on samples of T. elegans from Rome (Lazio). All T. caroni specimens had 2n = 48 chromosomes, but the 8th and 17th pairs differed morphologically between specimens from Capri and Terracina and those from Sicily. The mitochondrial 16S rRNA analysis grouped Sicilian and non-Sicilian populations of T. caroni in distinct subclades. Superimposing karyological data on their phylogenetic tree suggests that possible chromosomal rearrangements occurred during the diversification of Trochoidea. Our findings provide karyological and molecular evidence for a diversification between Sicilian and non-Sicilian populations of T. caroni. Furthermore, NOR-FISH revealed hybridisation signals on the 16th chromosome pair in both T. caroni and T. elegans (tribe Trochoideini). Similar NOR localisation has also been identified in Cernuella virgata (tribe Cernuellini), suggesting that it was inherited from the common ancestor of Trochoideini and Cernuellini.