How do some birds get such bright red feathers?

Date: May 19, 2016

Source: Cell Press

In the bird world, the color red has special significance. Many species use red signals to attract mates or deter rivals, adding the color to their beaks, feathers, or bare skin. Generally speaking, as far as many birds are concerned, redder is better. Now, two teams of researchers have independently identified an enzyme-encoding gene that allows some bird species to convert yellow pigments from their diets into that remarkable red. Their findings are reported on May 19 in Current Biology.

"To produce red feathers, birds convert yellow dietary pigments known as carotenoids into red pigments and then deposit them in the feathers," says Miguel Carneiro of Universidade do Porto in Portugal. "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," adds Nick Mundy of the University of Cambridge. "Our findings fill this gap and open up many future avenues for research on the evolution and ecology of red coloration in birds."

Carneiro's team, including Joseph Corbo of Washington University School of Medicine in St. Louis and Geoffrey Hill of Auburn University, made their discovery thanks to canary fanciers who crossed a yellow canary with a red siskin almost 100 years ago, producing the world's first red canary. In the new study, the researchers compared the genome sequences of yellow and red canaries to red siskins in search of the gene responsible for the birds' color differences.

Their search led them to a cytochrome P450 enzyme, dubbed CYP2J19. Further analysis of the gene's expression showed that the enzyme is expressed at high levels in the skin and liver of red factor canaries, strongly implicating it as the enzyme responsible for red coloration.

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