Genomics on a warming sea: structure and adaptation of the Mediterranean loggerhead (Caretta caretta) nesting populations

Considering the current scenario of biodiversity crisis, it is crucial to understand how populations are structured and their adaptation drivers to aid management and conservation. In this context, sea turtles are predicted to be heavily impacted by climate change, causing feminisation of the populations and decreasing hatchling survival rates. These effects can be exacerbated in the Mediterranean, as it is predicted that global warming will exceed global trends. Here we genotyped 243 individuals from 11 nesting populations of the Mediterranean loggerhead se turtle ( Caretta caretta ) using 2bRAD, obtaining a panel of 5,998 curated SNPS. We then combined this genomic information of with environmental, behavioural and reproductive data to investigate their population structure and understand their mechanisms of adaptation. We found substantial genetic differentiation among almost all rookeries, with a major break separating Greek locations, and a second break separating Libya from the Levantine locations. This genetic structuring, caused by male and female philopatry, was also shaped by adaptation with strong genomic signals associated with all phenotypic and environmental variables tested. A conservation prioritisation analysis, to identify the areas with higher priority for protection, concluded that protecting all rookeries should be considered a priority, as some areas are key to retain the genetic diversity and adaptive potential of the Mediterranean region, while others play a crucial role maintaining connectivity that is fundamental for the long-term survival of this vulnerable species. This case study exemplifies the potential of genomics to unveil key information for species of conservation concern.