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Free keywords:
philopatry; local adaptation; mitochondrial DNA; microsatellites; major histocompatibility complex; loggerhead sea turtle (Caretta caretta)
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.
