Spatial and temporal analysis of the genetic diversity of three small delphinid species in the Italian waters using ancient DNA

This study has investigated the genetic diversity of three Mediterranean dolphin species, Stenella coeruleoalba, Delphinus delphis and Tursiops truncatus. This inquiry has been reached through the analysis of the ancient DNA (aDNA) extracted from the bone powder of museum specimens, musealized during the last two centuries. The subsequent PCR amplification and sequencing of the aDNA extracted, comparing it with GenBank retrieved sequences of the target species, has allowed to address taxonomic issues including the categorization of sampled individuals into the correctly assigned, the misidentified and the previous unassigned sampled specimens as well as the identification of potential hybrids. If the molecular analysis wasn’t resolutive for the specimen’s identification, an integrated morphometric-molecular approach has been adopted. Together with the molecular taxonomy for the three target species, essential for the identification of the museum specimens, the spatiotemporal shifts of the species’ genetic diversity have been also investigated by species-specific haplotype diversity, mismatch distribution analysis and single-haplotype frequencies temporal distribution across 200 years. The species-specific haplotype networks revealed three different topologies, corresponding to three distinct evolutive histories for the target species, while the mismatch distributions showed a demographic expansion for all the three target species, even if the low polymorphism of the marker could make all the distribution appear as skewed. Finally, the comparative analysis on single-haplotype frequencies temporal distribution pointed out a genetic decay for both D. delphis, but not for S. coeruleoalba and T. truncatus. However, the short length of the Cytochrome B marker of the mitochondrial DNA used in this study, along with the unbalancing in some of the chosen time intervals for some target species, make its results preliminary, requiring for an implementation of this work.