The macroevolutionary consequences of the association between frugivory and carotenoid-dependent plumage coloration in passerine birds

Biotic interactions influence evolutionary pathways, impacting diversification positively and negatively. Here, we examine the coevolutionary dynamics between frugivorous diets and carotenoid-dependent plumage coloration in passerine birds-a highly diverse order in which nearly half of species exhibit carotenoids in their plumage. Plumage coloration is crucial for species recognition and mate choice. As birds cannot synthesize carotenoids, they must obtain them from the diet. We analyze data from 90% of passerines and explore correlations between frugivory, a key carotenoid source, plumage coloration, and diversification rates. Our Bayesian analysis reveals a strong evolutionary correlation between frugivory and the presence of carotenoid plumage coloration. However, Bayesian state-dependent speciation and extinction models showed that neither frugivory nor carotenoid coloration independently correlates with heightened diversification. Results are unchanged when we analyze the combination of both traits, challenging the conventional assumption of increased speciation driven by frugivory in species with carotenoid-dependent plumage coloration. These findings underscore the complexity of trait interactions in shaping evolutionary trajectories and the importance of hidden states in modeling diversification. While not confirming a direct link between correlated evolution and diversification, our study sheds light on the intricate interplay between ecological interactions and evolutionary patterns in passerine birds.