Department of Ecology and Evolutionary Biology, Ramaley N122, UCB 334, University of Colorado at Boulder, Boulder, CO 80309, USA.
Horm Behav. 2013 Sep;64(4):665-72. doi: 10.1016/j.yhbeh.2013.08.006. Epub 2013 Sep 4.
Sexually selected traits confer greater reproductive benefits to individuals with more elaborate forms of the signal. However, whether these signals convey reliable information about the physiology underlying trait development remains unknown in many species. The steroid hormone corticosterone (CORT) mediates important physiological and behavioral processes during the vertebrate stress response, and CORT secretion itself can be modulated by melanocortins. Thus, sexually selected melanin-based plumage coloration could function as an honest signal of an individual's ability to respond to stressors. This hypothesis was tested in North American barn swallows, Hirundo rustica erythrogaster, where males with darker ventral plumage color exhibit higher phaeomelanin content and are more successful at reproduction. Because reproductive behavior occurs months after plumage signals are developed, we also addressed the potential temporal disconnect of physiological state during trait development and trait advertisement by analyzing three different measurements of CORT levels in adult males during the breeding season (trait advertisement) and in nestling males while they were growing their feathers (trait development). Variation in adult plumage color did not predict baseline or stress-induced CORT, or stress responsiveness. Likewise, there was no relationship between nestling plumage color and any of the CORT measurements, but heavier nestlings had significantly lower baseline CORT. Our finding that a predominantly phaeomelanin-based trait is unrelated to circulating CORT suggests that phaeomelanin and eumelanin signals may convey different physiological information, and highlights the need for further study on the biochemical links between the hypothalamic-pituitary-adrenal (HPA) axis and the production of different melanin-based pigments.
性选择特征赋予具有更复杂信号形式的个体更大的繁殖益处。然而，在许多物种中，这些信号是否能传递关于特征发育背后生理机能的可靠信息仍然未知。类固醇激素皮质酮（CORT）在脊椎动物应激反应中介导重要的生理和行为过程，而 CORT 的分泌本身可以被黑色素细胞调节。因此，基于黑色素的性选择羽毛颜色可能作为个体应对应激源能力的诚实信号。这个假设在北美家燕（Hirundo rustica erythrogaster）中得到了检验，在这种鸟类中，腹部羽毛颜色较深的雄性具有更高的真黑色素含量，并且在繁殖方面更成功。由于繁殖行为发生在羽毛信号形成后的数月，我们还分析了繁殖季节成年雄性（特征展示）和正在生长羽毛的雏鸟雄性（特征发育）的三种不同 CORT 水平测量值，以解决生理状态在特征发育和特征展示之间潜在的时间脱节问题。成年羽毛颜色的变化不能预测基础或应激诱导的 CORT 或应激反应性。同样，雏鸟羽毛颜色与任何 CORT 测量值之间也没有关系，但体重较大的雏鸟基础 CORT 显著降低。我们的发现表明，主要基于真黑色素的特征与循环 CORT 无关，这表明真黑色素和真黑色素信号可能传递不同的生理信息，并强调了需要进一步研究下丘脑-垂体-肾上腺（HPA）轴和不同黑色素基颜料产生之间的生化联系。
