Carotenoid-based ornaments predict survival in male but not female birds: A meta-analysis

Many vertebrates exhibit colorful ornaments generated by carotenoid pigments that presumably evolved as signals under sexual selection. To function as sexual signals, carotenoid-based colored ornaments should accurately reveal an individual's quality, commonly defined as fitness potential, which includes the ability to survive. We performed a meta-analysis to test the association between the expression level of carotenoid-based ornaments and longevity estimates in birds, the taxon with the largest body of evidence. We detected a significant positive correlation in males but not in females. This contrasts with recent meta-analytic work showing a positive association between carotenoid-based colored traits and avian fecundity in both sexes. The link to survival was consistent across colorations produced by enzymatically transformed pigments (mostly red ketocarotenoids) and those based on dietary yellow carotenoids, suggesting that the association holds across physiological mechanisms involved in ornament production. In summary, our study reveals sex-specific selection in the evolution of carotenoid-based ornaments.