Variation in pigmentation often underlies many tractable and interesting questions in evolutionary biology; such as speciation, adaptation and sexual selection. Understanding the genetic mechanisms underlying colour variation can provide great insight into the evolutionary processes governing this variation, how it arose and how it is maintained. Using an experimental cross and SNP genotyping we set out to identify the loci underlying three zebra finch plumage variants.
We chose three autosomal recessive zebra finch mutants – yellow beak, black cheek and penguin and crossed these with wild-type zebra finch. We have three generations of birds and have typed these with SNPs spread evenly across the genome.
This project was funded by the Biotechnology and Biological Sciences Research Council.
Identification of the molecular mechanisms underlying red beak colouration.
Red plumage and skin is used widely by birds to attract mates and during male competition. The colour is produced by converting yellow carotenoids, which are ingested by the bird into the characteristic red ketocarotenoids and adding this to the feathers, skin or beaks. By mating mutant zebra finch birds that lacked red colouration in the beak (known as the yellowbeak mutation) with wild type birds we were able to identify the locus, or genetic location of the genes that are responsible for this red colouration. In this genetic region we found two genes that are likely to encode the ketolase enzyme, CYP2J19A and CYP2J19B. Birds lacking red beaks had a different version of this gene. In normal red beaked birds these genes are expressed in the beak, skin and retina. In the yellowbeak birds the gene is only expressed in the retina. As a result the mutant birds have yellow beaks unlike the normal bright red beak characteristic of zebra finches. The gene we identified belongs to a family of genes, the cytochrome P450 oxidases, which are involved in detoxification. In sexual selection, red colour is thought to signal individual quality and one way it can do this is if the amount of red colour is related to other physiological processes, like detoxification. Our results, which link a detoxification gene to carotenoid metabolism, shed new light on this old hypothesis about the honesty of signalling.
Mundy N, Stapley J, Bennison C, Tucker R, Twyman H, Kang-Wook K, Burke T, Birkhead TR, Andersson S, Slate J. (In press) Red ketocarotenoid pigmentation in the zebra finch is controlled by a cytochrome P450 gene cluster. Current Biology 26:1435-1440 Link to paper