title: Carotenoid-dependent signals and the evolution of plasma carotenoid levels in birds.
abstract: Sexual selection has resulted in a wide array of ornaments used in mate choice, and such indicator traits signal quality honestly when they bear costs, precluding cheating. Carotenoid-dependent coloration has attracted considerable attention in this context, because investing carotenoids in coloration has to be traded off against its physiological functions; carotenoids are antioxidants and increase immunocompetence. This trade-off is hypothesized to underlie the honesty of carotenoid-dependent coloration, signaling the "handicap" of allocating carotenoids away from somatic maintenance toward sexual display. Utilizing recent advances in modeling adaptive evolution, we used a comparative approach to investigate the evolution of plasma carotenoid levels using a species-level phylogeny of 178 bird species. We find that the evolutionary optimum for carotenoid levels is higher in lineages that evolved carotenoid-dependent coloration, with strong attraction toward this optimum. Hence, carotenoids do not appear to be limiting, given that higher carotenoid levels readily evolve in response to the evolution of carotenoid-dependent coloration. These findings challenge the assumption that carotenoids are a scarce resource and thus also challenge the hypothesis that physiological resource value of carotenoids underlies honesty of carotenoid-dependent traits. Therefore, the comparative evidence suggests that other factors, such as the acquisition and incorporation of carotenoids, are involved in maintaining signal honesty.
authors.affiliation: Behavioural Biology, Centre for Life Sciences, University of Groningen, PO Box 11103, 9700CC, Groningen, The Netherlands.
authors.forename: Mirre J P
authors.initials: MJ
authors.lastname: Simons
authors.forename: Rafael
authors.initials: R
authors.lastname: Maia
authors.forename: Bas
authors.initials: B
authors.lastname: Leenknegt
authors.forename: Simon
authors.initials: S
authors.lastname: Verhulst
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D005075:Biological Evolution; D001717:Birds / Q000378:metabolism / Q000502:physiology*; D002338:Carotenoids / Q000097:blood* / Q000378:metabolism; D010802:Phylogeny; D010858:Pigmentation / Q000502:physiology*; D012727:Sex Characteristics; D015398:Signal Transduction
chemical_list: D000975:Antioxidants; D002338:Carotenoids