Oxidative stress is related to both melanin‐ and carotenoid‐based ornaments in the common yellowthroat

Abstract

Summary 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.