Correlation between whistles variability and phylogenetic distance in Mediterranean delphinids (Delphinidae)

Whistles are found in the vocal repertoire of most delphinids (Cetacea: Delphinidae) and may encode species and population identity, with acoustic similarities potentially reflecting phylogenetic relationships. This study is the first to correlate species-specific whistles characteristics and genetic distance in the five dolphin species regularly observed in the Mediterranean Sea (Dd: Delphinus delphis, Gg: Grampus griseus, Gm: Globicephala melas, Sc: Stenella coeruleoalba, Tt: Tursiops truncatus), to determine whether vocalizations follow a similar evolutionary trajectory. Mitochondrial gene sequences 12S, 16S, and cytochrome c oxidase subunit I (cox1) were retrieved from online databases (e.g. GenBank). Six acoustic parameters (e.g., max and min frequency, duration) of whistles were gathered from the available literature. We performed pairwise comparison between sound divergence and genetic diversity. Specifically, genetic distance matrix was obtained using the Kimura two-parameter (K2P) method (bootstrap variance estimation, 1000 replications) based on the concatenated dataset for all used molecular markers. Acoustic distance matrix was built from the species’ means of acoustic parameters using hierarchical clustering based on Manhattan distances. In the reconstructed phylogenetic tree, Dd, Sc and Tt formed a distinct clade, separate from Gg and Gm, highlighting an evolutionary divergence between the Delphininae and Globicephalinae subfamilies. Most species pairs (e.g., Gm - Tt and Dd - Sc) exhibited relatively consistent patterns in both genetic and acoustic divergences. However, Gg showed large differences in acoustic distances compared to genetic distances with all other dolphin species, being phylogenetically close to Gm, while emitting whistles acoustically similar to Tt. While a correlation exists between genetic and acoustic distances, whistles diversity does not always mirror genetic divergence, suggesting that acoustic signals of delphinids may be shaped by factors beyond genetics, such as environmental, ecological, or social conditions.