Without genetic variation, species cannot cope with changing environments, and evolution does not proceed. In endangered species, adaptive potential may be eroded by decreased population sizes and processes that further reduce gene flow such as philopatry and local adaptations. Here, we focused on the philopatric and endangered loggerhead sea turtle (Caretta caretta) nesting in Cape Verde as a model system to investigate the link between adaptive potential and philopatry. We produced a dataset of three complementary genomic regions to investigate female philopatric behaviour (mitochondrial DNA), male-mediated gene flow (microsatellites) and adaptive potential (major histocompatibility complex, MHC). Results revealed genetically distinct nesting colonies, indicating remarkably small-scale philopatric behaviour of females. Furthermore, these colonies also harboured local pools of MHC alleles, especially at the margins of the population's distribution, which are therefore important reserves of additional diversity for the population. Meanwhile, directional male-mediated gene flow from the margins of distribution sustains the adaptive potential for the entire rookery. We therefore present the first evidence for a positive association between philopatry and locally adapted genomic regions. Contrary to expectation, we propose that philopatry conserves a high adaptive potential at the margins of a distribution, while asymmetric gene flow maintains genetic connectivity with the rest of the population.

Dispersal during juvenile life stages drives the life-history evolution and dynamics of many marine vertebrate populations. However, the movements of juvenile organisms, too small to track using conventional satellite telemetry devices, remain enigmatic. For sea turtles, this led to the paradigm of the 'lost years' since hatchlings disperse widely with ocean currents. Recently, advances in the miniaturization of tracking technology have permitted the application of nano-tags to track cryptic organisms. Here, the novel use of acoustic nano-tags on neonate loggerhead turtle hatchlings enabled us to witness first-hand their dispersal and behaviour during their first day at sea. We tracked hatchlings distances of up to 15 km and documented their rapid transport (up to 60 m min 21 ) with surface current flows passing their natal areas. Tracking was complemented with laboratory observations to monitor swimming behaviours over longer periods which highlighted (i) a positive correlation between swimming activity levels and body size and (ii) population-specific swimming behaviours (e.g. nocturnal inactivity) suggesting local oceanic conditions drive the evolution of innate swimming behaviours. Knowledge of the swimming behaviours of small organisms is crucial to improve the accuracy of ocean model simulations used to predict the fate of these organisms and determine resultant population-level implications into adulthood.

BackgroundIn evolutionary and conservation biology, parasitism is often highlighted as a major selective pressure. To fight against parasites and pathogens, genetic diversity of the immune genes of the major histocompatibility complex (MHC) are particularly important. However, the extensive degree of polymorphism observed in these genes makes it difficult to conduct thorough population screenings.MethodsWe utilized a genotyping protocol that uses 454 amplicon sequencing to characterize the MHC class I in the endangered loggerhead sea turtle (Caretta caretta) and to investigate their evolution at multiple relevant levels of organization.ResultsMHC class I genes revealed signatures of trans-species polymorphism across several reptile species. In the studied loggerhead turtle individuals, it results in the maintenance of two ancient allelic lineages. We also found that individuals carrying an intermediate number of MHC class I alleles are larger than those with either a low or high number of alleles.ConclusionsMultiple modes of evolution seem to maintain MHC diversity in the loggerhead turtles, with relatively high polymorphism for an endangered species.

As biodiversity worldwide is decreasing, to preserve adaptive potential, the importance of maintaining species' genetic and trait diversities is increasing. An efficient foraging strategy is a critical trait for an organism's fitness, as it affects its physiology and reproduction. Understanding such strategies is especially relevant for species with long feeding migrations such as sea turtles. Using carbon and nitrogen stable isotopes combined with mitochondrial sequencing, we explored the diversity of feeding strategies in genetically differentiated nesting groups of loggerhead sea turtles (Caretta caretta) within the Cape Verde Archipelago. Here, we reveal a pattern where turtles from most islands use two distinct oceanic feeding strategies, including one putatively linked to a 15 N-enriched zone of the West African upwelling area. On the Eastern island of Boavista, an additional third strategy exists used by turtles feeding mostly neritically. Contrary to previous paradoxical assumptions, oceanic turtles, that represent the vast majority of the population, are not smaller than neritic turtles and therefore do not seem to feed in a suboptimal environment. Our results also suggest that the number of feeding strategies may correlate with demography, whereby a greater feeding strategy diversity matches demographic signs of recent expansion after a population bottleneck for turtles nesting on the island of Boavista. Overall, the feeding ecology of Cape Verde loggerhead turtles is complex and likely shaped by an interaction between environmental and population parameters. Our results stress the importance of conservation efforts to prevent loss of critical diversity in endangered species.