A window on the genetics of evolution: MC1R and plumage colouration in birds

Abstract

Melanins are a ubiquitous component of plumage colouration in birds and serve a wide variety of functions. Although the genetic control of melanism has been studied in chickens and other domestic species, little was known about the molecular genetics of melanin distribution in wild birds until recently. Studies have now revealed that a single locus, the melanocortin-1 receptor (MC1R) locus, is responsible for melanic polymorphisms in at least three unrelated species: the bananaquit, the snow goose and the arctic skua. Results show that melanism was a derived trait and allow other evolutionary inferences about the history of melanism to be made. The role of MC1R in plumage patterning is surprisingly diverse among different species. The conserved molecular basis for the evolution of melanism in birds and several other vertebrates is probably related to low pleiotropic effects at the MC1R.

Figure 1

Relationship between MC1R genotype and melanic phenotype in three birds. Population locations are as follows: Mt Hartman, Grenada; Cape Henrietta, Hudson Bay, Canada; Slettnes, Norway.

Figure 2

MC1R sequence variants associated with plumage or hair colour change in birds and mammals. Extracellular is up. Single letter amino acid code is used to indicate substitutions and Δ indicates deletions. Substitutions associated with eumelanism are indicated by solid colouring, those associated with reduction in eumelanin (often along with increased phaeomelanin) are indicated by horizontal hatching. The R160W substitution is associated both with melanism in rock pocket mice and red hair in humans. There are small differences in MC1R length in different species and sites are numbered after the species they refer to. For mammalian references see Majerus & Mundy (2003).