The taste for the beautiful: influence of diet on the evolution of plumage in tanagers

The diversity of animal shapes and colors raises questions about the mechanisms by which species acquire complex phenotypes considering that they evolve under both natural and sexual selection. Tanagers employ a diversity of signals in social interactions which, coupled with diverse diets that include fruits and flowers, make them an excellent group for studying how diet influences the evolution of communication signals. Using Bayesian linear mixed models, plumage reflectance data for 291 tanager species (∼77% of species), and appropriate techniques for compositional diet data, we show that percentage increases in frugivory and/or nectarivory dietary components are associated with higher hue disparity scores (a proxy of plumage coloration complexity). Additionally, evolutionary decreases in the percentage of seeds and arthropods, coupled with increases in fruits, are related to higher color complexity. The presence of structural coloration in plumage was related to high hue disparity and frugivory, but carotenoid-based coloration-contrary to expectations-was not associated with either. Our results support the hypothesis that the link between diet and plumage coloration arose not from a physiological constraint but from sensory (perceptual) biases of frugivores and nectarivores for detecting colorful baits in the forest, which resulted in preferences for chromatically diverse feather patterns.