Red color in birds: It’s all in the genes

Using colors for variety of things isn’t new to the animal kingdom and one of the colors used by birds for communication, attracting the opposite sex, among other things is red.

But how does this color get produced in birds? That’s a question that researchers at University of Cambridge and other universities asked and they found the answer in genes. Researchers at the university reveal through a new study published in the Journal Current Biology that they have, for the first time ever, identified genes that allow some bird species to produce the red pigment that plays such a critical role in attraction and mating.

Authors of the study note that quite a few bird species including Zebra finch get their yellow pigments from diet of seeds, or insects in the case of other bird species. Up until now scientists believed that the birds may have a way of converting these yellow dietary pigments into the red pigments that color the beaks, feathers or bare skin of many species. However, the mechanism for this process was unclear.

Nick Mundy from Cambridge’s Department of Zoology, along with colleagues from the University of Gothenburg and University of Sheffield, compared the gene sequences of wild, red-beaked zebra finches with captive finches that had a mutant, recessive gene causing yellow beaks. They identified a cluster of three genes in the wild finches that were either missing or mutated in this genetic region in the ‘yellowbeak’ birds.

These genes encode enzymes called cytochrome P450s, which play an important role in breaking down and metabolising toxic compounds, primarily in the liver of vertebrates. Red color in birds is thought to signal individual genetic quality, and the researchers argue that one way it can do this is if the amount of red color relates to other beneficial physiological processes, such as detoxification.

Researchers found the specific expression of one or more of the identified ‘red’ gene cluster in the tissues where the red pigments were deposited: the beak, the tarsus in the bird’s feet – as well as in the retina.

The structure of retinas in the eye includes cone-shaped photoreceptor cells. Unlike mammals, avian retinal cones contain a range of brightly-colored oil droplets, including green, yellow and red. These oil droplets allow birds to see many more colors than mammals.

Mundy says that the newly-discovered genetic links between red beaks and feathers and the internal red retina droplets suggest that producing red pigment evolved for color vision before it developed a function for external display – as, while red oil eye droplets are ubiquitous across bird species, external reds are only patchily distributed.

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