Roulin A, Dijkstra C
University of Cambridge, Department of Zoology, Downing Street, CB2 3EJ Cambridge, UK.
Heredity (Edinb). 2003 May;90(5):359-64. doi: 10.1038/sj.hdy.6800260.
Knowledge of the mechanism underlying the expression of melanin-based sex-traits may help us to understand their signalling function. Potential sources of inter-individual variation are the total amount of melanins produced but also how biochemical precursors are allocated into the eumelanin and phaeomelanin pigments responsible for black and reddish-brown colours, respectively. In the barn owl (Tyto alba), a eumelanin trait (referred to as 'plumage spottiness') signals immunocompetence towards an artificially administrated antigen and parasite resistance in females, whereas a phaeomelanin trait ('plumage coloration') signals investment in reproduction in males. This raises the question whether plumage coloration and spottiness are expressed independent of each other. To investigate this question, we have studied the genetics of these two plumage traits. Crossfostering experiments showed that, for each trait, phenotypic variation has a strong genetic component, whereas no environmental component could be detected. Plumage coloration is autosomally inherited, as suggested by the similar paternal-to-maternal contribution to offspring coloration. In contrast, plumage spottiness may be sex-linked inherited (in birds, females are heterogametic). That proposition arises from the observation that sons resembled their mother more than their father and that daughters resembled only their father. Despite plumage coloration and spottiness signalling different qualities, these two traits are not inherited independent of each other, darker birds being spottier. This suggests that the extent to which coloration and spottiness are expressed depends on the total amount of melanin produced (with more melanin leading to a both darker and spottier plumage) rather than on differential allocation of melanin into plumage coloration and spottiness (in such a case, darker birds should have been less spotted). A gene controlling the production of melanin pigments may be located on sex-chromosomes, since the phenotypic correlation between coloration and spottiness was stronger in males than in females.
了解基于黑色素的性别特征表达背后的机制，可能有助于我们理解它们的信号功能。个体间变异的潜在来源不仅包括所产生黑色素的总量，还包括生化前体如何分别分配到负责黑色和红棕色的真黑素和褐黑素色素中。在仓鸮（Tyto alba）中，一种真黑素特征（称为“羽毛斑点”）向雌性发出针对人工接种抗原的免疫能力和寄生虫抗性的信号，而一种褐黑素特征（“羽毛颜色”）向雄性发出繁殖投入的信号。这就引出了一个问题，即羽毛颜色和斑点是否相互独立表达。为了研究这个问题，我们研究了这两种羽毛特征的遗传学。交叉寄养实验表明，对于每一种特征，表型变异都有很强的遗传成分，而未检测到环境成分。羽毛颜色是常染色体遗传的，这从父本和母本对后代颜色的贡献相似可以看出。相比之下，羽毛斑点可能是性连锁遗传的（在鸟类中，雌性是异配性别）。这一观点源于以下观察结果：儿子与其母亲的相似程度超过与其父亲的相似程度，而女儿只与其父亲相似。尽管羽毛颜色和斑点发出不同的信号，但这两个特征并非相互独立遗传，颜色较深的鸟斑点更多。这表明颜色和斑点的表达程度取决于所产生黑色素的总量（黑色素越多，羽毛颜色越深且斑点越多），而不是黑色素在羽毛颜色和斑点之间的差异分配（在这种情况下，颜色较深的鸟斑点应该更少）。由于颜色和斑点之间的表型相关性在雄性中比在雌性中更强，控制黑色素色素产生的基因可能位于性染色体上。
