Spatio-temporal patterns of genetic diversity in the Mediterranean striped dolphin (Stenella coeruleoalba)

Comparing the genetic composition of wild animals between geographic regions with distinct environments is common in evolutionary studies. However, genetic composition can also change through time in response to environmental changes but studies examining this are carried out less often. In this study, we characterize striped dolphin genetic composition in the Mediterranean Sea across both geography and time. We provide genotype data for 15 microsatellite loci and 919 bp of mtDNA control region, collected over 21 years across all main Mediterranean Sea basins. We investigated spatial genetic structure using both classical and Bayesian population structure methods, and compared it with temporal patterns of genetic change using time-series statistics. We integrated the temporal datasets with known environmental pressures and data on social structure, to infer potential drivers of observed changes. Geographic analyses suggest weak differentiation for striped dolphin in the Mediterranean Sea, with evidence for a recent expansion. Temporal analyses show significant cyclical fluctuations in genetic composition over 21 years, which correspond well with recurrent morbillivirus epizootics. Similarly, social group composition shows changes in the relative number of juveniles and adults per group, and an overall increase in the number of adults per group relative to juveniles over the time period. We suggest that the observed changes in genetic and group composition could relate to specific dynamics of morbillivirus resistance. Overall, our study highlights the importance of tracking long-term genetic variation and the potential for this species as a model in studying genetic adaptation to environmental stress.