Association between melanism, physiology and behaviour: A role for the melanocortin system

Abstract

The melanocortin system is implicated in the expression of many phenotypic traits. Activation of the melanocortin MC 1 receptor by melanocortin hormones induces the production of brown/black eumelanic pigments, while activation of the four other melanocortin receptors affects other physiological and behavioural functions including stress response, energy homeostasis, anti-inflammatory and sexual activity, aggressiveness and resistance to oxidative stress. We recently proposed the hypothesis that some melanocortin-physiological and -behavioural traits are correlated within individuals. This hypothesis predicts that the degree of eumelanin production may, in some cases, be associated with the regulation of glucocorticoids, immunity, resistance to oxidative stress, energy homeostasis, sexual activity, and aggressiveness. A review of the zoological literature and detailed experimental studies in a free-living population of barn owls (Tyto alba) showed that indeed melanic coloration is often correlated with the predicted physiological and behavioural traits. Support for predictions of the hypothesis that covariations between coloration and other phenotypic traits stem from pleiotropic effects of the melanocortin system raises a number of theoretical and empirical issues from evolutionary and pharmacological point of views.

Genetic colour polymorphism is associated with avian malarial infections

“…In birds, genetic colour polymorphism-defined as a highly heritable variation in expressed plumage coloration that is independent of age and sex-is often associated with variation in life-history traits, including physiology, behaviour and immunity [3,4]. These associations may result from pleiotropic effects of genes regulating melanogenesis, such as the melanocortin-1-receptor (Mc1r).…”

Gloger's rule in North American Barn Owls

“…On museum skin specimens, we counted and measured the size of black eumelanic feather spots, as well as measuring pheomelanin-based coloration, which varies from white to dark red. In European Barn Owls (T. a. alba, T. a. guttata), these three plumage traits are genetically correlated with behavioral and physiological processes (Roulin and Ducrest 2011). For instance, smaller-spotted and redder pheomelanic owls have a higher appetite , and larger-spotted owls are more resistant to parasitism and to various sources of stress that induce a rise in glucocorticoids (Roulin et al 2000, Almasi et al 2012.…”

“…These pleiotropic genes may therefore account for the covariation between melanin-based coloration, behaviour, and physiology (Roulin and Ducrest 2011), regardless of whether melanin-based coloration is involved in camouflage or whether melanin pigments participate in thermoregulation or in the protection of the integument against parasites and abrasion. Therefore, not only selection exerted on coloration but also selection exerted on genetically correlated physiological or behavioral traits may account for geographic variation.…”

Malpigmentation in <i>Diagramma pictum</i> and <i>Pardachirus marmoratus</i> Collected from the Arabian Sea Coasts of Oman

“…Such variation in partial melanic pigmentation is could be due to the causes stated by Roulin and Ducrest (2011). They found that maneuvering of the genes of the melanocortin system or of their products will have significant effects on a set of characters.…”