Department of Ecology & Evolution, University of Lausanne, Lausanne, Switzerland.
J Evol Biol. 2011 Oct;24(10):2241-7. doi: 10.1111/j.1420-9101.2011.02353.x. Epub 2011 Jul 11.
The control mechanisms and information content of melanin-based colourations are still debated among evolutionary biologists. Recent hypotheses contend that molecules involved in melanogenesis alter other physiological processes, thereby generating covariation between melanin-based colouration and other phenotypic attributes. Interestingly, several molecules such as agouti and glutathione that trigger the production of reddish-brown pheomelanin have an inhibitory effect on the production of black/grey eumelanin, whereas other hormones, such as melanocortins, have the opposite effect. We therefore propose the hypothesis that phenotypic traits positively correlated with the degree of eumelanin-based colouration may be negatively correlated with the degree of pheomelanin-based colouration, or vice versa. Given the role played by the melanocortin system and glutathione on melanogenesis and resistance to oxidative stress, we examined the prediction that resistance to oxidative stress is positively correlated with the degree of black colouration but negatively with the degree of reddish colouration. Using the barn owl (Tyto alba) as a model organism, we swapped eggs between randomly chosen nests to allocate genotypes randomly among environments and then we measured resistance to oxidative stress using the KRL assay in nestlings raised by foster parents. As predicted, the degree of black and reddish pigmentations was positively and negatively correlated, respectively, with resistance to oxidative stress. Our results reveal that eumelanin- and pheomelanin-based colourations can be redundant signals of resistance to oxidative stress.
黑色素生物色素的控制机制和信息含量仍然是进化生物学家争论的话题。最近的假设认为，参与黑色素生成的分子会改变其他生理过程，从而在黑色素生物色素和其他表型属性之间产生共变。有趣的是，几种分子，如触发红棕色真黑色素产生的阿育它和谷胱甘肽，对黑/灰色真黑色素的产生有抑制作用，而其他激素，如黑素皮质素，则有相反的效果。因此，我们提出了这样一个假设：与真黑色素生物色素着色程度呈正相关的表型特征可能与真黑色素生物色素着色程度呈负相关，或者反之亦然。鉴于黑素皮质系统和谷胱甘肽在黑色素生成和抵抗氧化应激方面的作用，我们检验了这样一个预测，即抵抗氧化应激与黑色着色程度呈正相关，但与红色着色程度呈负相关。我们使用仓鸮（Tyto alba）作为模型生物，在随机选择的巢之间交换鸡蛋，将基因型随机分配到环境中，然后使用 KRL 测定法在由养父母抚养的雏鸟中测量对氧化应激的抵抗力。正如预测的那样，黑色和红色色素沉着的程度分别与对氧化应激的抵抗力呈正相关和负相关。我们的结果表明，真黑色素和真黑色素生物色素着色可以是抵抗氧化应激的冗余信号。
