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

1. Male ornaments are hypothesized to signal the ability of males to produce an effective immune response without extensive oxidative stress and damage to DNA. 2. 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. 3. 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 hemolysis 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. 4. 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. 5. 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.

1. 学界假说认为，雄性饰羽（male ornaments）可传递雄性在避免过度氧化应激（oxidative stress）与DNA损伤的前提下，产生有效免疫应答的能力。
2. 我们以普通黄喉地莺（Geothlypis trichas）雄性个体为研究对象验证该假说，该物种雄性具有两类饰羽：基于真黑素（eumelanin）沉积的黑色面部面罩状饰羽，以及基于类胡萝卜素（carotenoid）沉积的黄色喉斑饰羽。在本研究种群中，仅黑色面罩状饰羽受到性选择（sexual selection）青睐。
3. 正如氧化应激假说所预测，拥有更大尺寸黑色面罩饰羽的雄性，其抗氧化应激能力更强——该结论通过体外（in vitro）实验测定红细胞对抗自由基诱导溶血的能力得以验证。此外，面罩饰羽尺寸更大的雄性，其体内谷胱甘肽（glutathione）水平往往更低，这一结果符合假说预期，因为谷胱甘肽会抑制真黑素合成。与之相对，面罩饰羽尺寸与血浆中测得的绝对氧化应激水平并无关联。
4. 尽管本研究种群中黄色喉斑饰羽未受到性选择作用，但喉斑尺寸更大、羽毛类胡萝卜素色度（carotenoid chroma）更高的雄性，其氧化应激水平依然更低。
5. 氧化应激假说最初是针对基于类胡萝卜素的饰羽提出的。然而本研究结果表明，即便在同一雄性个体中，基于类胡萝卜素与真黑素的羽饰，均有可能传递雄性抵抗或调控氧化应激的能力。