The evolutionary pathways for local adaptation in mountain hares
Résumé
Understanding the evolution of local adaptations is a central aim of evolutionary biology
and key for the identification of unique populations and lineages of conservation
relevance. By combining RAD sequencing and whole-genome
sequencing, we identify
genetic signatures of local adaptation in mountain hares (Lepus timidus) from isolated
and distinctive habitats of its wide distribution: Ireland, the Alps and Fennoscandia.
Demographic modelling suggested that the split of these mountain hares occurred
around 20 thousand years ago, providing the opportunity to study adaptive evolution
over a short timescale. Using genome-wide
scans, we identified signatures of extreme
differentiation among hares from distinct geographic areas that overlap with area-specific
selective sweeps, suggesting targets for local adaptation. Several identified
candidate genes are associated with traits related to the uniqueness of the different
environments inhabited by the three groups of mountain hares, including coat colour,
ability to live at high altitudes and variation in body size. In Irish mountain hares, a
variant of ASIP, a gene previously implicated in introgression-driven
winter coat colour
variation in mountain and snowshoe hares (L. americanus), may underlie brown
winter coats, reinforcing the repeated nature of evolution at ASIP moulding adaptive
seasonal colouration. Comparative genomic analyses across several hare species suggested
that mountain hares’ adaptive variants appear predominantly species-specific.
However, using coalescent simulations, we also show instances where the candidate
adaptive variants have been introduced via introgressive hybridization. Our study
shows that standing adaptive variation, including that introgressed from other species,
was a crucial component of the post-glacial
dynamics of species.
Domaines
Evolution [q-bio.PE]
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