Meeting Abstract
Carotenoid coloration is the one of the most frequently studied ornamental traits in animals. Many studies of carotenoid coloration are focused on the associations between dietary intake of carotenoids, measures of performance such as immunocompetence and oxidative state, and production of ornamental coloration. Such studies commonly involve supplementing the diets of captive birds with carotenoids. In many cases, however, the amount of carotenoids administered is extrapolated from studies of other species of different body mass. We used meta-analysis to synthesize published studies where bird diets were supplemented with varying concentrations of carotenoids to elucidate the relationship between carotenoid supplementation, color, and immune function. Allometric scaling equations estimated the per-gram carotenoid consumption of subjects, and meta-regression contrasted the impact of differences in adjusted carotenoid intake on differences in coloration, plasma carotenoid level, and immunocompetence between supplemented and control groups of birds. Additional subgroup analyses discriminated effects of carotenoid supplementation between species with ornamental color in their bills or legs and those with colored plumage ornaments. Supplementation effects varied among ornament types, but there was significant heterogeneity in responses across studies and species. Our results emphasize the importance of using dosage trials or measuring actual carotenoid intake to validate that supplementation levels are appropriate for a particular study species and experimental design.
