title: Viability is associated with melanin-based coloration in the barn swallow (Hirundo rustica).
abstract: Pigmentation of body surface in animals can have multiple determinants and accomplish diverse functions. Eumelanin and pheomelanin are the main animal pigments, being responsible of yellow, brownish-red and black hues, and have partly common biosynthetic pathways. Many populations of vertebrates show individual variation in melanism, putatively with large heritable component. Genes responsible for eu- or pheomelanogenesis have pleiotropic but contrasting effects on life-history traits, explaining the patterns of covariation observed between melanization and physiology (e.g. immunity and stress response), sexual behavior and other characters in diverse taxa. Yet, very few studies in the wild have investigated if eu- and pheomelanization predict major fitness traits like viability or fecundity. In this correlative study, by contrasting adult barn swallows (Hirundo rustica) matched for age, sex, breeding site, and year and date of sampling, we show that males but not females that survived until the next year had paler, relatively more eu- than pheomelanic pigmentation of ventral body feathers. Better performance of individuals that allocate relatively more to eumelanogenesis was expected based on previous evidence on covariation between eumelanic pigmentation and specific traits related to immunity and susceptibility to stress. However, together with the evidence of no covariation between viability and melanization among females, this finding raises the question of the mechanisms that maintain variation in genes for melanogenesis. We discuss the possibility that eu- and pheomelanization are under contrasting viability and sexual selection, as suggested by larger breeding and sperm competition success of darker males from other barn swallow subspecies.
authors.affiliation: Department of Biosciences, University of Milan, Milan, Italy. nicola.saino@unimi.it
authors.forename: Nicola
authors.initials: N
authors.lastname: Saino
authors.forename: Maria
authors.initials: M
authors.lastname: Romano
authors.forename: Diego
authors.initials: D
authors.lastname: Rubolini
authors.forename: Roberto
authors.initials: R
authors.lastname: Ambrosini
authors.forename: Manuela
authors.initials: M
authors.lastname: Caprioli
authors.forename: Aldo
authors.initials: A
authors.lastname: Milzani
authors.forename: Alessandra
authors.initials: A
authors.lastname: Costanzo
authors.forename: Graziano
authors.initials: G
authors.lastname: Colombo
authors.forename: Luca
authors.initials: L
authors.lastname: Canova
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
mesh_terms: D000818:Animals; D005241:Feathers / Q000378:metabolism*; D005260:Female; D016014:Linear Models; D008297:Male; D008543:Melanins / Q000378:metabolism*; D009026:Mortality; D010858:Pigmentation; D012737:Sex Factors; D046388:Swallows / Q000033:anatomy & histology / Q000378:metabolism*
chemical_list: D008543:Melanins