Data from: Pleiotropy in the melanocortin system: expression levels of this system are associated with melanogenesis and pigmentation in the tawny owl (Strix aluco)

The adaptive function of melanin-based coloration is a long-standing debate. A recent genetic model suggested that pleiotropy could account for covariations between pigmentation, behaviour, morphology, physiology and life history traits. We explored whether the expression levels of genes belonging to the melanocortin system (MC1R, POMC, PC1/3, PC2 and the antagonist ASIP), which have many pleiotropic effects, are associated with melanogenesis (through variation in the expression of the genes MITF, SLC7A11, TYR, TYRP1) and in turn melanin-based coloration. We considered the tawny owl (Strix aluco) because individuals vary continuously from light to dark reddish, and thus, colour variation is likely to stem from differences in the levels of gene expression. We measured gene expression in feather bases collected in nestlings at the time of melanin production. As expected, the melanocortin system was associated with the expression of melanogenic genes and pigmentation. Offspring of darker reddish fathers expressed PC1/3 to lower levels but tended to express PC2 to higher levels. The convertase enzyme PC1/3 cleaves the POMC prohormone to obtain ACTH, while the convertase enzyme PC2 cleaves ACTH to produce α-melanin-stimulating hormone (α-MSH). ACTH regulates glucocorticoids, hormones that modulate stress responses, while α-MSH induces eumelanogenesis. We therefore conclude that the melanocortin system, through the convertase enzymes PC1/3 and PC2, may account for part of the interindividual variation in melanin-based coloration in nestling tawny owls. Pleiotropy may thus account for the covariation between phenotypic traits involved in social interactions (here pigmentation) and life history, morphology, behaviour and physiology.基于黑色素的体色的适应功能是一个长期存在的学术争议。近期一项遗传模型研究表明，多效性（pleiotropy）可解释色素沉着、行为、形态、生理及生活史性状间的协变关系。我们探究了属于黑皮质素系统（melanocortin system）的基因——包括黑皮质素1受体（MC1R）、阿黑皮素原（POMC）、前蛋白转化酶1/3（PC1/3）、前蛋白转化酶2（PC2）以及拮抗剂ASIP，这些基因具有广泛的多效性作用——其表达水平是否与黑色素生成（通过MITF、SLC7A11、TYR、TYRP1等基因的表达变异介导）相关，并进而影响基于黑色素的体色。我们选择灰林鸮（Strix aluco）作为研究对象，因其个体体色从浅到深红褐色呈连续渐变，故其体色变异可能源于基因表达水平的差异。我们在雏鸟黑色素生成阶段采集其羽基样本以检测基因表达水平。正如预期，黑皮质素系统与黑色素生成相关基因的表达及体色显著相关。体色较深的红褐色父本的后代，其PC1/3的表达水平更低，而PC2的表达水平则更高。前蛋白转化酶PC1/3可切割阿黑皮素原（POMC）以生成促肾上腺皮质激素（ACTH），而前蛋白转化酶PC2则可切割ACTH以产生α-促黑素细胞激素（α-MSH）。促肾上腺皮质激素（ACTH）可调节糖皮质激素（glucocorticoids）——一类调控应激反应（stress responses）的激素——的分泌，而α-促黑素细胞激素（α-MSH）则可诱导真黑色素生成（eumelanogenesis）。因此我们认为，黑皮质素系统通过前蛋白转化酶PC1/3和PC2，可部分解释灰林鸮雏鸟基于黑色素的体色的个体间变异。由此，多效性或许可以解释社会互动相关表型性状（本研究中的色素沉着）与生活史、形态、行为及生理之间的协变关系。