SRA

The green turtle (Chelonia mydas) is a migratory species that connects geographically distant areas while maintains population differentiation due to philopatry. Recent observations indicate an expansion of the species' distribution with sporadic nests discovered in new Mediterranean locations and sexually mature individuals recorded in the western Mediterranean. To assess these events, we constructed individual 2b-RAD libraries from 3 green turtle Regional Management Units (RMU) and build a genomic baseline: Northwest Atlantic, East Atlantic and Mediterranean (N = 15; 5 individuals from each RMU). Additionally, we genotyped 7 hatchlings from 3 sporadic Mediterranean nests and 3 out of 4 adult adults tagged with satellite telemetry in the western basin, obtaining genotypes from 10 unknown origin individuals. In brief, we i) assessed current genetic differentiation among RMUs and ii) combined genetic and tagging information to identify the potential source population of unknown origin individuals. All the potential colonisers were satisfactory assigned to one of the source RMUs using genomic data. We detected that nests were events from distant populations: Poilão (East Atlantic RMU) and Akamas (Mediterranean), showing that this starting colonisation has multiple origins. The three adult individuals with genomic data also originated in these two RMUs, while the remaining individual lacking genomic data exhibited an Atlantic mtDNA haplotype. Our results combining telemetry and genomic information provide for the first time exit trajectories of Atlantic individuals from the Mediterranean and movements within the Western basin, thereby unveiling new migration routes for both Atlantic and Mediterranean populations. The results suggest an incipient double colonisation probably associated with climate change, by two distant populations that have not yet mixed in the past.