Department of Evolutionary Ecology, Museo Nacional de Ciencias Naturales (CSIC), E-28006 Madrid, Spain.
J Exp Biol. 2010 Sep 15;213(Pt 18):3127-30. doi: 10.1242/jeb.045096.
Conspicuous traits produced by melanin deposition in integuments are often involved in visual communication. The information content of melanin-based signals is unclear as their expression is tightly controlled by genes and, apparently, is less dependent on individual condition. In birds, high heritabilities have been attributed to melanin-based plumages, often on the basis of egg-swapping manipulations (cross-fostering experiments). However, it is well known that female birds can differentially transfer testosterone to the egg yolk. Furthermore, high testosterone levels have been related to high oxidative stress. As we recently found that oxidative stress experienced during development influences the expression of melanin-based traits, here we manipulated the level of yolk testosterone in great tits (Parus major) to assess the influence of this maternal effect on the expression of the black breast stripe, a well-known melanin-based signal. We predicted that fledglings hatched from eggs with high testosterone levels will not only show larger black stripes but also experience changes in their antioxidant machinery. Indeed, the size of the black stripe of great tits hatched from testosterone-injected eggs was almost double that of controls. Furthermore, the same individuals showed a trend to higher levels of circulating antioxidants, which suggests an adaptive response against some testosterone-induced oxidative challenge.
皮肤中黑色素沉积所产生的明显特征通常与视觉通讯有关。基于黑色素的信号的信息含量尚不清楚，因为它们的表达受基因的严格控制，而且显然不太依赖个体状况。在鸟类中，黑色素羽色的遗传力很高，这通常是基于换蛋操作（交叉孵化实验）得出的。然而，众所周知，雌性鸟类可以将睾丸激素差异地转移到蛋黄中。此外，高睾丸激素水平与高氧化应激有关。由于我们最近发现发育过程中经历的氧化应激会影响基于黑色素的特征的表达，因此我们在大山雀（Parus major）中操纵蛋黄中的睾丸激素水平，以评估这种母体效应对黑色胸部条纹表达的影响，这是一种众所周知的基于黑色素的信号。我们预测，从高睾丸激素水平的卵中孵化出来的雏鸟不仅会有更大的黑色条纹，而且还会经历其抗氧化机制的变化。事实上，从注射了睾丸激素的卵中孵化出来的大山雀的黑色条纹大小几乎是对照组的两倍。此外，同一批个体的循环抗氧化剂水平也呈现出上升趋势，这表明它们对一些睾丸激素诱导的氧化应激具有适应性反应。
