Lack of polymorphism at the MC1R wild-type allele and evidence of domestic alleles introgression across European wild boar populations.

Domestication promotes the emergence of novel phenotypic and behavioural traits in
domesticated animals compared to their wild ancestors. We analysed variation at the
melanocortin receptor I (MC1R) and nuclear receptor subfamily 6, group A, member 1 (NR6A1)
genes in European wild boar populations, two loci which have been under strong artificial
selection during domestication. These loci influence coat colour and number of vertebrae,
respectively.
A total of 145 wild boars were sampled throughout Europe, to evaluate frequency and spatial
distribution of domestic alleles and patterns of hybridization between wild and domestic forms.
Most of the wild boars (94%) were homozygous for the European wild-type (E+) MC1R allele.
We did not observe any synonymous substitution in the European E+ allele, confirming its
monomorphism even in areas known to be hotspots of wild boar genetic diversity. The remaining
wild boars (6%) showed genetic introgression of three different European domestic alleles. No
Asian MC1R allele was found in our sample.
Furthermore, domestic NR6A1 alleles were observed in 6% of wild boars. Considering jointly the
two loci analyzed, 11% of boars, sampled all over Europe, showed signs of recent or past
introgression in their genome.
These data agree with previous investigations on other molecular markers, confirming that,
compared to Asian conspecifics, European wild boars have a relatively low genetic diversity,
which is locally increased by the introgression of allelic variants from the domestic counterpart.