Range expansion in the land snail species Carinigera buresi (Clausiliidae): Long-distance dispersal by ancient marble transport?

Abstract

The clausiliid Carinigera buresi has a distribution that, considering its low vagility, is enigmatically disjunct. Carinigera buresi pharsalica occurs in Thessaly in central Greece, over 200 km outside the main range of C. buresi in NE Greece-SW Bulgaria. This range disjunction has led to the hypothesis that in antiquity the ancestors of C. buresi pharsalica were transported by the marble trade from NE Greece to Thessaly. To explore this hypothesis, we included samples from the NE Greek island of Thasos (the only area within the range of C. buresi from which marble was widely transported in antiquity) in a time-calibrated molecular phylogeny of C. buresi. Maximum likelihood (GARLI) and time-calibrated Bayesian (BEAST) analyses of mitochondrial cytochrome c oxidase subunit I (COI) from samples collected throughout the range of C. buresi indicate that the ancestral C. buresi pharsalica COI lineage reached Thessaly not from Thasos, but from the NE Greek mainland. This happened between 1,740 and 83,000 yr BP according to the BEAST analyses. Although this time interval does not entirely pre-date the earliest phase of marble transport in the region, we consider this mode of dispersal unlikely for two reasons: (1) our data show that C. buresi pharsalica must be older than estimated on the basis of geological calibration points; (2) our findings indicate that the dispersal event that brought C. buresi pharsalica to Thessaly did not follow ancient marble transport routes. We suggest dispersal via floating objects or aerial dispersal by birds as alternative hypotheses to dispersal by the historic marble trade. Unexpectedly, our phylogenetic analyses also showed the COI haplotype of C. buresi from the city of Kavala to be nested among COI haplotypes from northern Thasos. This suggests possible human-aided dispersal of C. buresi from Thasos to Kavala.