Data from: Oxidative stress is related to both melanin- and carotenoid-based ornaments in the common yellowthroat

Male ornaments are hypothesized to signal the ability of males to produce
an effective immune response without extensive oxidative stress and damage
to DNA. We examined this hypothesis in male common yellowthroats
(Geothlypis trichas), which have two ornaments, a black (eumelanin-based)
facial mask and a yellow (carotenoid-based) bib. In our study population,
only the black mask is sexually selected. As predicted by the oxidative
stress hypothesis, males with larger black masks were more resistant to
oxidative stress, as measured by an in vitro assay of the resistance of
erythrocytes to haemolysis by free radicals. Furthermore, males with
larger masks also tended to have lower levels of glutathione, which was
predicted because glutathione inhibits eumelanin production. In contrast,
mask size was not related to absolute levels of oxidative stress measured
in the plasma. Although the yellow bib is not under sexual selection in
our population, males with larger bibs and feathers with greater
carotenoid chroma had lower levels of oxidative stress. The oxidative
stress hypothesis was first proposed for carotenoid-based ornaments.
However, our results suggest that, even in the same individuals,
carotenoid and eumelanin-based plumage ornaments may both signal the
ability of males to resist or manage oxidative stress.

研究假说认为，雄性动物的装饰特征可传递其在产生有效免疫应答的同时，避免过度氧化应激与DNA损伤的能力。我们针对雄性普通黄喉地莺（Geothlypis trichas）检验了这一假说，该物种具有两类装饰特征：基于真黑色素（eumelanin）的黑色面部面罩，以及基于类胡萝卜素（carotenoid）的黄色喉羽。在我们的研究种群中，仅黑色面部面罩受到性选择作用。正如氧化应激假说所预测的那样，拥有更大黑色面罩的雄性个体抗氧化应激能力更强，该结果通过体外实验测定红细胞抵抗自由基溶血的能力得到验证。此外，面罩更大的雄性个体谷胱甘肽（glutathione）水平往往更低，这一结果符合预测，因为谷胱甘肽会抑制真黑色素的合成。相较而言，面罩尺寸与血浆中测得的氧化应激绝对水平并无关联。尽管在本研究种群中黄色喉羽未受到性选择作用，但拥有更大喉羽及类胡萝卜素色度更高羽毛的雄性个体，其氧化应激水平更低。氧化应激假说最初是针对基于类胡萝卜素的装饰特征提出的。然而我们的研究结果表明，即便在同一雄性个体身上，基于类胡萝卜素与基于真黑色素的羽毛装饰特征，均可传递其抵抗或调控氧化应激的能力。