Sex‐specific allelic transmission bias suggests sexual conflict at MC 1R

Sexual conflict arises when selection in one sex causes the displacement of the other sex from its phenotypic optimum, leading to an inevitable tension within the genome – called intralocus sexual conflict. Although the autosomal melanocortin‐1‐receptor gene ( MC 1R ) can generate colour variation in sexually dichromatic species, most previous studies have not considered the possibility that MC 1R may be subject to sexual conflict. In the barn owl ( Tyto alba ), the allele MC 1 R WHITE is associated with whitish plumage coloration, typical of males, and the allele MC 1 R RUFOUS is associated with dark rufous coloration, typical of females, although each sex can express any phenotype. Because each colour variant is adapted to specific environmental conditions, the allele MC 1 R WHITE may be more strongly selected in males and the allele MC 1 R RUFOUS in females. We therefore investigated whether MC 1R genotypes are in excess or deficit in male and female fledglings compared with the expected Hardy–Weinberg proportions. Our results show an overall deficit of 7.5% in the proportion of heterozygotes in males and of 12.9% in females. In males, interannual variation in assortative pairing with respect to MC 1R explained the year‐specific deviations from Hardy–Weinberg proportions, whereas in females, the deficit was better explained by the interannual variation in the probability of inheriting the MC 1 R WHITE or MC 1 R RUFOUS allele. Additionally, we observed that sons inherit the MC 1 R RUFOUS allele from their fathers on average slightly less often than expected under the first Mendelian law. Transmission ratio distortion may be adaptive in this sexually dichromatic species if males and females are, respectively, selected to display white and rufous plumages.