DELPHISTORY - Historical changes in the specific, ecological and genetic diversity of small mediterranean dolphins: contribution to the definition of trends and sustainability thresholds for the conservation of the mediterranean cetaceans.

The Mediterranean Sea, one of the most significant biodiversity hotspots, has undergone significant ecological transformations driven by increasing anthropogenic pressures such as overfishing, pollution, and habitat degradation. Cetaceans are among the marine organisms most impacted. This study focuses on three small delphinid species, the common dolphin Delphinus delphis, the striped dolphin Stenella coeruleoalba, and the bottlenose dolphin Tursiops truncatus, that have experienced major demographic and ecological shifts over the last two centuries. Understanding historical population dynamics and ecological preferences is challenging due to the scarcity of long-term ecological data and the limited scientific reliability of historical literature, which was often anecdotal and affected by taxonomic uncertainty. This PhD project applies a multidisciplinary approach combining geometric morphometrics, molecular analyses of ancient DNA, and stable isotope analyses to reconstruct historical ecology and assess species and genetic diversity of Mediterranean delphinids. More than 400 osteological specimens from the 19th to the 21st century, housed in 26 museum collections across the Mediterranean basin, were collected and sampled. An integrative taxonomic study validated the identification of museum samples, enabling a comprehensive assessment of dolphin species diversity over the past 200 years. Stable isotopes of carbon (δ¹³C), nitrogen (δ¹⁵N), and sulphur (δ³⁴S) were analysed to trace temporal changes in ecology and habitat use. Results reveal significant shifts in isotopic niches and trophic interactions, especially for the common dolphin, in which an ecological niche shift coincided with the demographic decline observed in the late 1960s. Complementary genomic analyses provided the first mitochondrial genomes of Mediterranean D. delphis and S. coeruleoalba, offering new insights into historical phylogeography. Overall, this study demonstrates the critical scientific value of museum collections for reconstructing the ecological and genetic history of marine mammals, contributing essential information for future conservation strategies.