Gene-Coded Enzyme Is The Reason For Redness In Birds: Study

Red birds can sometimes raise red flags, even as the special color is typically part of beaks, feathers and skins of birds. Two studies show the enzyme that converts yellow pigments in birds to red.

"To produce red feathers, birds convert yellow dietary pigments known as carotenoids into red pigments and then deposit them in the feathers," said Miguel Carneiro of the Universidade do Porto in Portugal and senior author of the first study. "Birds also accumulate these same red pigments in one of the cone photoreceptor types in their retina to enhance color vision. We discovered a gene that codes for an enzyme that enables this yellow-to-red conversion in birds."

"It was known that some birds have the ability to synthesize red ketocarotenoids from the yellow carotenoids that they obtain in their diet, but the gene or enzyme involved, and its anatomical location, have been obscure," added Nick Mundy of the University of Cambridge and first author of the second study. "Our findings fill this gap and open up many future avenues for research on the evolution and ecology of red coloration in birds."

When Carneiro and his team studied the genome sequences of yellow and red canaries and compared information to red siskins, the scientists showed that the expression of the cytochrome P450 enzyme, also called gene CYP2J19, is linked with red.

Mundy's experiment identified the cytochrome P450 gene cluster even as standard zebra finches with red beaks and mutant zebra finches with yellow beaks were identified. Zebra finches show a total of three cytochrome P450 genes, while multiple mutations of this area were found in yellowbeak birds.

The CYP2J19 is part of a family of genes that also has a crucial role to play in detoxification. How then did it evolve into playing its current role?

"In sexual selection, red color is thought to signal individual quality, and one way it can do this is if the type or amount of pigmentation is related to other physiological processes, like detoxification," said Staffan Andersson of the University of Gothenburg and co-author of the second study. "Our results, which link a detoxification gene to carotenoid metabolism, may shed new light on the debated honesty of carotenoid-based signals."

Both studies were published in the journal Current Biology.