Lack of polymorphism at MC1R wild-type allele and evidence of domestic allele 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.