Résumé
Background: The extent to which selection determines interspecific
patterns of genetic exchanges enlightens the role of adaptation in
evolution and speciation. Often reported extensive interspecific
introgression could be selection-driven, but also result from demographic
processes, especially in cases of invasive species replacements, which can
promote introgression at their front. Because invasion and selective
sweeps similarly mold variation, population genetics evidence for
selection can only be gathered in an explicit demographic framework. The
Iberian hare, Lepus granatensis, displays in its northern range extensive
mitochondrial DNA introgression from L. timidus, an arctic/boreal species
that it replaced locally after the last glacial maximum. We use
whole-genome sequencing to infer geographic and genomic patterns of
nuclear introgression and fit a neutral model of species replacement with
hybridization, allowing us to evaluate how selection influenced
introgression genome-wide, including for mtDNA. Results: Although the
average nuclear and mtDNA introgression patterns are strongly contrasted,
they fit a single neutral model of post-glacial invasive replacement of
timidus by granatensis. Outliers of elevated introgression include several
genes related to immunity, spermatogenesis, and mitochondrial metabolism.
Introgression is reduced on the X-chromosome and in low recombining
regions. Conclusion: General nuclear and mtDNA patterns of introgression
can be explained by purely demographic processes. Hybrid incompatibilities
and interplay between selection and recombination locally modulate levels
of nuclear introgression. Selection promoted introgression of some genes
involved in conflicts, either interspecific (parasites) or possibly
cytonuclear. In the latter case, nuclear introgression could mitigate the
potential negative effects of alien mtDNA on mitochondrial metabolism and
male-specific traits.