Data from: Sex-specific allelic transmission bias suggests sexual conflict at MC1R

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 (MC1R) can generate colour variation in sexually dichromatic species, most previous studies have not considered the possibility that MC1R may be subject to sexual conflict. In the barn owl (Tyto alba), the allele MC1RWHITE is associated with whitish plumage coloration, typical of males, and the allele MC1RRUFOUS 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 MC1RWHITE may be more strongly selected in males and the allele MC1RRUFOUS in females. We therefore investigated whether MC1R 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 MC1R 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 MC1RWHITE or MC1RRUFOUS allele. Additionally, we observed that sons inherit the MC1RRUFOUS 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.

性冲突（sexual conflict）指某一性别的选择压力致使另一性别的表型最适值发生偏移，进而引发基因组内不可避免的张力——即基因座内性冲突（intralocus sexual conflict）。尽管常染色体黑皮质素-1受体基因（MC1R）可在两性异形色物种中引发体色变异，但此前多数研究未考虑MC1R可能受到性冲突作用的可能性。
在仓鸮（Tyto alba）中，MC1RWHITE等位基因与雄性典型的浅色羽毛色泽相关，MC1RRUFOUS等位基因则与雌性典型的深赤褐色羽毛色泽相关，尽管两性均可表现出任意一种表型。由于每种色泽变体均适配特定的环境条件，MC1RWHITE等位基因在雄性中可能受到更强的选择压力，而MC1RRUFOUS等位基因则在雌性中受选择更强。因此，我们探究了相较于预期哈迪-温伯格比例（Hardy–Weinberg proportions），仓鸮雌雄幼鸟的MC1R基因型比例是否存在过剩或缺失。
我们的研究结果显示，雄性杂合子比例整体较预期缺失7.5%，雌性则缺失12.9%。在雄性个体中，针对MC1R的选型交配（assortative pairing）年际变化可解释各年份偏离哈迪-温伯格比例的现象；而在雌性个体中，杂合子缺失现象更可通过MC1RWHITE或MC1RRUFOUS等位基因的遗传概率年际变化得到合理解释。此外，我们观察到，雄性子代从父本处遗传得到MC1RRUFOUS等位基因的概率，平均略低于孟德尔第一定律（first Mendelian law）的预期水平。若该两性异形色物种分别选择雄性展现浅色羽毛、雌性展现赤褐色羽毛，则传递比畸变（transmission ratio distortion）在此类物种中可能具备适应性意义。