Résumé
Urbanization is a growing concern challenging the evolutionary potential
of wild populations by reducing genetic diversity and imposing new
selection regimes affecting many key fitness traits. However, genomic
footprints of urbanization have received little attention so far. Using
RAD sequencing, we investigated the genome-wide effects of urbanization on
neutral and adaptive genomic diversity in 140 adult great tits Parus major
collected in locations with contrasted urbanization levels (from a natural
forest to highly urbanized areas of a city (Montpellier, France).
Heterozygosity was slightly lower in the more urbanized sites compared to
the more rural ones. Low but significant effect of urbanization on genetic
differentiation was found, at the site-level but not at the nest-level,
indicative of the geographic scale of urbanization impact and of the
potential for local adaptation despite gene flow. Gene-environment
association tests identified numerous SNPs with small association scores
to urbanization, distributed across the genome, from which a subset of 97
SNPs explained up to 81% of the variance in urbanization, overall
suggesting a polygenic response to selection in the urban environment.
These findings open stimulating perspectives for broader applications of
high-resolution genomic tools on other cities and larger sample sizes to
investigate the consistency of the effects of urbanization on the spatial
distribution of genetic diversity and the polygenic nature of
gene-urbanization association.