Data from: Effect of the MC1R gene on sexual dimorphism in melanin-based colorations

Variants of the melanocortin-1 receptor (MC1R) gene results in abrupt, naturally selected color morphs. These genetic variants may differentially affect sexual dimorphism if one morph is naturally selected in the two sexes but another morph is naturally or sexually selected only in one of the two sexes (e.g., to confer camouflage in reproductive females or confer mating advantage in males). Therefore, the balance between natural and sexual selection can differ between MC1R variants, as suggest studies showing inter-specific correlations between sexual dimorphism and the rate of non-synonymous vs. synonymous amino acid substitutions at the MC1R. Surprisingly, how MC1R is related to within-species sexual dimorphism, and thereby to sex-specific selection, has not yet been investigated. We tackled this issue in the barn owl (Tyto alba), a species showing pronounced variation in the degree of reddish pheomelanin-based coloration and in the number and size of black feather spots. We found that a valine (V) to isoleucine (I) substitution at position 126 explains up to 30% of the variation in the three melanin-based color traits and in feather melanin content. Interestingly, MC1R genotypes also differed in the degree of sexual color dimorphism, with individuals homozygous for the II MC1R-variant being 2 times redder and 2.5 times less sexually dimorphic than homozygous individuals for the VV MC1R-variant. These findings support that MC1R interacts with the expression of sexual dimorphism and suggest that a gene with major phenotypic effects and weakly influenced by variation in body condition can participate in sex-specific selection processes.

黑皮质素1受体（melanocortin-1 receptor, MC1R）基因的变异会产生由自然选择塑造的骤然分化的自然色型。若某一色型在两性中均受自然选择，而另一色型仅在单一性别中受自然选择或性选择（例如赋予繁殖雌性伪装优势，或赋予雄性交配优势），则这类遗传变异可能会对性二态性产生差异化影响。因此，自然选择与性选择之间的平衡可能因MC1R变异而异，已有研究表明性二态性与MC1R位点非同义与同义氨基酸替换速率之间存在种间相关性。令人意外的是，目前尚未有研究探讨MC1R与种内性二态性的关联，进而揭示其与性别特异性选择的关系。我们针对这一问题以仓鸮（Tyto alba）为研究对象，该物种基于褐黑素的红棕色羽色变异以及黑色羽斑的数量与大小均存在显著差异。研究发现，126号位缬氨酸（V）向异亮氨酸（I）的替换可解释三种黑色素相关羽色性状以及羽毛黑色素含量中高达30%的变异。有趣的是，不同MC1R基因型的性二态程度存在差异：携带II型MC1R纯合变异的个体，其羽色红度为VV型MC1R纯合个体的2倍，而性二态程度仅为后者的2.5倍。上述研究结果表明，MC1R与性二态性的表达存在相互作用，同时提示一个具有显著表型效应且受身体状况变异影响较弱的基因，可参与性别特异性选择过程。