Abstract
World marine ecosystems are experiencing unprecedented anthropic pressures inducing rapid environmental changes that threaten the persistence of wild species and their local populations. Hence, understanding the effects of genetic variability and dispersal capacities on marine population persistence is a key issue for the conservation of biodiversity. My PhD work had two main objectives: (i) evaluate the spatial distribution and drivers of genetic variation across coastal marine fish populations, and (ii) estimate the response of populations to climate changes in order to better understand their ability to persist.First, by performing a synthesis of published literature on 31 Mediterranean fish species, I showed that ecological traits related to mobility and population size strongly influence the level of within-population genetic diversity across species. Then, I studied the drivers of spatial genetic variation using genetic data from 727 individuals of the stripped red-mullet (Mullus surmuletus) collected in 72 sites around the Mediterranean Sea, and grouped into 47 pools genotyped for 1153 single nucleotide polymorphism (SNP) markers. Seascape genetic analyses showed that larval dispersal predominantly structures M. surmuletus genetic variation at intermediate and local spatial scales (<1000 km), whereas geographic isolation, due to population demographic history or adaptation, is the main driver at larger spatial scale. Lastly, studying the adaptive genetic variation of M. surmuletus using genome scan revealed a potential adaptive response of this species to the East-West gradient in salinity across the Mediterranean Sea.Subsequently, using a demo-genetic model to simulate coral population dynamics and resilience across the Indo-pacific corals, I showed that the process of ‘evolutionary rescue’ can help genotypes adapted to warm ocean waters to move and migrate between populations thanks to larval connectivity. Evolutionary rescue can thus promote the persistence of populations by allowing them to adapt to environmental changes that would otherwise lead to population declines or even local extinctions.Finally, all of these results highlighted the need to better consider connectivity and the evolutionary potential of species in conservation strategies, in order to maximize their resilience capacity and long-term persistence in the face of more severe environmental crises.