Meeting Abstract
Carotenoid-based coloration in bird species has become a classic example of an honest signal of male quality used in female mate assessment; however, the mechanisms linking carotenoid coloration to male immunocompetence and/or oxidative stress maintenance remain contested. The prevailing hypothesis to explain the honesty of carotenoid-based coloration posits that carotenoid pigments are a limited resource that must be differentially allocated either to ornamental coloration or to boosting beneficial physiological processes such that only healthy birds of good condition can afford to produce a high quality ornament. In this study, we use a novel system of canaries (Serinus canaria) with knock-out mutations to directly test the importance of carotenoid pigments to immune and antioxidant processes and to search for a “cost” of allocating pigments to ornamentation. During the annual molt—when yellow canaries are actively depositing carotenoids into their feathers—we compared measures of immunocompetence and oxidative stress in canaries with and without circulating carotenoids (carotenoid-rich vs. carotenoid-free birds), and canaries with and without ornamental feather coloration (yellow vs. white canaries). Interestingly, we found no significant differences in antibody production to a novel antigen (a measure of humoral immunity), plasma bacterial killing capacity (innate immunity), or measures of blood-based oxidative damage and antioxidant capacity between canaries with different carotenoid availability or ornamental usage. Our results raise important questions regarding the hypotheses that carotenoid pigments are essential to proper physiological function, and that the honesty of carotenoid coloration is maintained by the costs of allocating the pigments to coloration.
