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.
Highlights
Coloration is a major target of natural selection as it can influence thermoregulation, and camouflage of prey and their predators, and mediates social and sexual communication
Several observational and experimental studies on model species or genetically engineered strains under artificial conditions have shown that melanogenesis and melanin-based pigmentation covary with a number of traits ranging from regulation of metabolism and energy homeostasis, to immunity, response to stressors mediated by the hypothalamic-pituitary-adrenal axis, social aggressiveness and sexual behavior [9]
Field Procedures We studied adult barn swallows breeding in 10 colonies
Summary
Coloration is a major target of natural selection as it can influence thermoregulation, and camouflage of prey and their predators, and mediates social and sexual communication. Several observational and experimental studies on model species or genetically engineered strains under artificial conditions have shown that melanogenesis and melanin-based pigmentation covary with a number of traits ranging from regulation of metabolism and energy homeostasis, to immunity, response to stressors mediated by the hypothalamic-pituitary-adrenal axis, social aggressiveness and sexual behavior [9]. In particular, has been shown to positively covary with traits related to social and sexual performance, resistance to stress, immunity and metabolism in wild vertebrates [9]. Detailed studies of the very few wild bird populations that have been investigated so far have provided consistent evidence for an association between physiological and behavioral traits and feather melanization [10,11,12,13,14,15], while information from other free-ranging vertebrates is sparse
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