Living on the edge: how philopatry maintains adaptive potential

Abstract

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.

Selection and sex‐biased dispersal in a coastal shark: the influence of philopatry on adaptive variation

“…Occurrence of philopatry in association with a nonrandom pattern of geographic variation in small genomic regions was reported recently (Stiebens et al . ) in a study of variation in MHC alleles among philopatric loggerhead turtles in the Cape Verde Archipelago. Both mtDNA haplotypes and MHC alleles were structured genetically among nesting islands, but only nuclear‐encoded microsatellites followed a geographic pattern, in this case one of isolation by distance indicative of restricted male dispersal.…”

Nano-tags for neonates and ocean-mediated swimming behaviours linked to rapid dispersal of hatchling sea turtles

“…[18,22,23] with (ii) recently trailed at sea acoustic tracking [31] and (iii) high-resolution ocean model data [32]. We focused on the Cape Verde Islands which host the World's third largest [33], and highly philopatric [34] nesting population of loggerhead turtles which are genetically isolated from other Atlantic and Mediterranean rookeries [12]. Owing to the oceanic location of these islands, this nesting aggregation is exposed to very different ocean current regimes than coastal mainland sites where studies into loggerhead turtle hatchling swimming behaviour have focused.…”

Evolution of MHC class I genes in the endangered loggerhead sea turtle (Caretta caretta) revealed by 454 amplicon sequencing

“…After amplification and cleaning of PCR product using EXoSap, sequences were loaded into an ABI 3730 Genetic Analyzer (Applied Biosystems, Darmstadt, Germany). For more details, see Stiebens et al [32]. Four different haplotypes were found: CcA1.3, CcA17.1, CcA17.2 and CcA2.1 following the Archie Carr Center for Sea Turtle Research nomenclature (http://accstr.ufl.edu/resources/mtdna-sequences/).…”

“…Recently, Monzon-Arguello et al [31] revealed the significant genetic divergence between the Cape Verde rookery and other Atlantic and Mediterranean rookeries. Furthermore, Stiebens et al [32] showed strong signs of philopatry at the island level, suggesting a complex structure of the rookery with independent colonies. Additionally, in Cape Verde, the fungus Fusarium solani was found to be the cause of infections in turtle eggs that accounted for over 80% of mortality in a challenged experiment [33], supporting the need to characterize immune relevant genes.…”