A red bird is a healthy bird study finds
A red bird is a healthy bird – a new study found that heightened redness in a bird’s colouring may be a sign of mate quality, it means that the bird is able to cleanse harmful substances from its body.
Right across the animal kingdom, especially among birds, the colour red is widely used for communication, frequently displayed to attract a mate. Male zebra finches (Taeniopygia guttata – formerly Poephila guttata) have a distinctive red beak – a sexually-selected trait – females are more attracted to males with redder beaks.
A new study on zebra finches by scientists from the Universities of Cambridge and Sheffield in England, and the University of Gothenburg in Sweden, has identified for the first time the genes that allow many species of birds to produce the red pigment that play such a key role in attracting a mate.
(Left) A wildtype male zebra finch with a distinctive red beak. (Right) A male zebra finch with the mutant ‘yellowbeak’ gene. (Image: Current Biology. Credit: Stuart Dennis)
Nick Mundy from Cambridge’s Department of Zoology and colleagues published details of their research and findings in the scientific journal Current Biology.
Red colour genes part of detoxification family of genes
These genes form part of a wider family of genes that also play a vital role in detoxification, which suggests that heightened redness may be a sign of male health – it indicates that the bird is able to cleanse harmful substances from its body.
This could explain what scientists called ‘honest signalling’, where a trait has evolved which is a genuine sign of better and fitter genes – in this case, the birds’ ability to deal with toxins.
Birds such as the zebra finch get their bright yellow pigments, known as carotenoids, from their diet of seeds, while other bird species may obtain theirs from insects.
Before this latest study, scientists knew that such birds must have a way of converting these yellow dietary pigments into red pigments – ketocarotenoids – which colour the feathers, beaks and bare skin of several species. However, nobody knew what the process was, that is, until now.
Dr. Mundy, University Reader in Evolutionary Genetics, along with Jessica Stapley from the University of Sheffield, and Staffan Andersson from the University of Gothenburg, compared the gene sequences of wild, red-beaked zebra finches with caged finches that had a mutant recessive gene, which makes them have yellow beaks.
In the wild finches, they identified a cluster of three genes, which were either mutated or missing in this genetic region in the caged or ‘yellowbeak’ birds.
These genes encode cytochrome P450s, enzymes which play a major role in breaking down and metabolising toxic compounds, primarily in vertebrates’ livers. These enzymes are well studied in humans, because they are strongly linked to drug metabolism.
Dr. Mundy said:
“It was known that birds have an unusual ability to synthesize red ketocarotenoids from the yellow carotenoids that they obtain in their diet, but the enzyme, gene or genes, and anatomical location have been obscure.”
“Our findings fill this gap and open up many future avenues for research on the evolution and ecology of red coloration in birds.”
Red signals genetic quality
Among birds, the colour red is thought to signal individual genetic quality. The authors suggest that one way it can do this is if the amount of red relates to other beneficial physiological processes, such as the elimination of toxins (detoxification).
Professor Andersson said:
“Our results, which link a detoxification gene to carotenoid metabolism, shed new light on this old hypothesis about the honesty of signaling.”
The authors found the specific gene expression of at least one of the identified ‘red’ gene clusters in the tissues that contained red pigments – in the tarsus in the birds’ feet, their beak and retina.
The retina contains cone-shaped photoreceptor cells. Birds’ retinal cones, unlike those of mammals, contain a range of brightly-coloured oil droplets, including red, yellow and green. These droplets allow birds to see several more colours than mammals.
The scientists say that the newly-discovered genetic links between red feathers and beaks and the internal red retina droplets suggest that producing red pigment evolved for seeing colours before it developed a function for external display, because red eye droplets are present across all bird species, while external reds are not.
Dr. Mundy said:
“It was quite a surprise that the same genes are involved both in seeing red colours and making red coloration.”
The researchers say they are currently working on the genetics of red colouration in African widowbirds and bishops, which show ‘spectacular differences among different species.’
The authors made the following comment in a Summary in the journal:
“Since cytochrome P450 enzymes include key detoxification enzymes, our results raise the intriguing possibility that red coloration may be an honest signal of detoxification ability.”
Citation: “Red Carotenoid Coloration in the Zebra Finch Is Controlled by a Cytochrome P450 Gene Cluster,”
Nicholas I. Mundy, Jessica Stapley, Clair Bennison, Rachel Tucker, Hanlu Twyman, Kang-Wook Kim, Terry Burke, Tim R. Birkhead, Staffan Andersson and Jon Slate. Current Biology. 19 May 2016. DOI: 10.1016/j.cub.2016.04.047.