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

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