title: Signaling stress? An analysis of phaeomelanin-based plumage color and individual corticosterone levels at two temporal scales in North American barn swallows, Hirundo rustica erythrogaster.
abstract: Sexually selected traits confer greater reproductive benefits to individuals with more elaborate forms of the signal. However, whether these signals convey reliable information about the physiology underlying trait development remains unknown in many species. The steroid hormone corticosterone (CORT) mediates important physiological and behavioral processes during the vertebrate stress response, and CORT secretion itself can be modulated by melanocortins. Thus, sexually selected melanin-based plumage coloration could function as an honest signal of an individual's ability to respond to stressors. This hypothesis was tested in North American barn swallows, Hirundo rustica erythrogaster, where males with darker ventral plumage color exhibit higher phaeomelanin content and are more successful at reproduction. Because reproductive behavior occurs months after plumage signals are developed, we also addressed the potential temporal disconnect of physiological state during trait development and trait advertisement by analyzing three different measurements of CORT levels in adult males during the breeding season (trait advertisement) and in nestling males while they were growing their feathers (trait development). Variation in adult plumage color did not predict baseline or stress-induced CORT, or stress responsiveness. Likewise, there was no relationship between nestling plumage color and any of the CORT measurements, but heavier nestlings had significantly lower baseline CORT. Our finding that a predominantly phaeomelanin-based trait is unrelated to circulating CORT suggests that phaeomelanin and eumelanin signals may convey different physiological information, and highlights the need for further study on the biochemical links between the hypothalamic-pituitary-adrenal (HPA) axis and the production of different melanin-based pigments.
authors.affiliation: Department of Ecology and Evolutionary Biology, Ramaley N122, UCB 334, University of Colorado at Boulder, Boulder, CO 80309, USA. Electronic address: bjenkins@uwyo.edu.
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Jenkins
authors.forename: Maren N
authors.initials: MN
authors.lastname: Vitousek
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Safran
mesh_terms: D000819:Animal Communication; D000818:Animals; D000831:Animals, Newborn; D003345:Corticosterone / Q000097:blood*; D005241:Feathers / Q000737:chemistry* / Q000378:metabolism; D008297:Male; D008543:Melanins / Q000032:analysis* / Q000378:metabolism; D010858:Pigmentation / Q000502:physiology*; D012149:Restraint, Physical / Q000523:psychology / Q000662:veterinary; D013315:Stress, Psychological / Q000097:blood / Q000378:metabolism; D046388:Swallows / Q000254:growth & development / Q000502:physiology*; D013997:Time Factors
chemical_list: D008543:Melanins; C016042:phaeomelanin; D003345:Corticosterone
keywords: Corticosterone; Eumelanin; Hirundo rustica; Hypothalamic–pituitary–adrenal (HPA) axis; Melanocortins; Phaeomelanin; Plumage color; Sexual selection; Stress response