Scientific Discovery Explains Why Birds Turn Red

Photo from Pixabay

In the world of birds, the color red plays a very important role. Red attracts mates, keeps rivals at bay and warns off predators; be it red beaks, plumes or feathers – the brighter a red, the better.

Two research teams have separately identified an enzyme in bird genes that allows some species to change yellow pigments from their diets to the preferred red. Miguel Carneiro of Universidade do Porto in Portugal explains, “To produce red feathers, birds convert yellow dietary pigments known as carotenoids into red pigments and then deposit them in the feathers. 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.”

Nick Mundy of the University of Cambridge concurs.

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

he says. “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 research team, which included Joseph Corbo of Washington University School of Medicine in St. Louis and Geoffrey Hill of Auburn University, went back to how the world’s first red canary was produced: some avian enthusiasts successfully crossbred a yellow canary with a red siskin finch close to a hundred years ago. The researchers went over the genome sequences of yellow and red canaries and compared them to genome sequences of red siskins to find the gene responsible for the birds’ different colors.

The researchers found the cytochrome P450 enzyme, dubbed CYP2J19. Upon further inspection, the enzyme appeared to be highly concentrated on the skin and liver of red factor canaries, strongly suggesting that it was the enzyme responsible for the bird’s red color.

Mundy’s team, which included Staffan Andersson of the University of Gothenburg and Jessica Stapley of the University of Sheffield, found cytochrome P450 enzyme by comparing normal zebra finches, which have a red beak, and mutant zebra finches, which have yellow beaks. They discovered that the regular zebra finches had three related cytochrome P450 genes, while multiple mutations showed in the same area in the finches with yellow beaks. They also found that the enzyme was expressed in very tiny amounts in the yellow beaks themselves.

These findings open a new dimension for studies on the red coloration of birds, according to the scientists. They also raise plenty of questions, as the gene belongs to a larger gene family that plays a part in detoxification.

“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,” Andersson explains. “Our results, which link a detoxification gene to carotenoid metabolism, may shed new light on the debated honesty of carotenoid-based signals.”

One thing that surprised the researchers was that this “red gene” is present in the genome sequences of many bird species, not just those with red feathers, says Corbo. “Diurnal birds appear to use this gene to produce red pigments in the retina to enhance color vision. However, only birds with red feathers additionally express the gene in their skin. These findings suggest that nearly all birds have the latent capacity to make red feathers, but in order to actually do so, they must evolve the means of expressing [this gene] in the skin in addition to the retina.”

Both team intend to pursue further studies into the gene, and into other bird species to determine if the same findings hold true and if there are any differences with other species.

The studies were reported in Current Biology.

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