̽��ֱ�� of Cambridge - Nick Mundy

‘Red gene’ in birds and turtles suggests dinosaurs had bird-like colour vision

fpjl2 — Wed, 03 Aug 2016 08:35:11 +0000

Earlier this year, scientists used zebra finches to pinpoint the gene that enables birds to produce and display the colour red.

Now, a new study shows the same ‘red gene’ is also found in turtles, which share an ancient common ancestor with birds. Both share a common ancestor with dinosaurs.

̽��ֱ��gene, called CYP2J19, allows birds and turtles to convert the yellow pigments in their diets into red, which they then use to heighten colour vision in the red spectrum through droplets of red oil in their retinas.

Birds and turtles are the only existing tetrapods, or land vertebrates, to have these red retinal oil droplets. In some birds and a few turtle species, red pigment produced by the gene is also used for external display: red beaks and feathers, or the red neck patches and rims of shells seen in species such as the painted turtle.

̽��ֱ��scientists mined the genetic data of various bird and reptile species to reconstruct an evolutionary history of the CYP2J19 gene, and found that it dated back hundreds of millions of years in the ancient archelosaur genetic line - the ancestral lineage of turtles, birds and dinosaurs.

̽��ֱ��findings, published today in the journal Proceedings of the Royal Society B, provide evidence that the ‘red gene’ originated around 250 million years ago, predating the split of the turtle lineage from the archosaur line, and runs right the way through turtle and bird evolution.

Scientists say that, as dinosaurs split from this lineage after turtles, and were closely related to birds, this strongly suggests that they would have carried the CYP2J19 gene, and had the enhanced ‘red vision’ from the red retinal oil.

This may have even resulted in some dinosaurs producing bright red pigment for display purposes as well as colour vision, as seen in some birds and turtles today, although researchers say this is more speculative.

“These findings are evidence that the red gene originated in the archelosaur lineage to produce red for colour vision, and was much later independently deployed in both birds and turtles to be displayed in the red feathers and shells of some species, going from seeing red to being red,” says senior author Dr Nick Mundy, from the ̽��ֱ�� of Cambridge’s Department of Zoology.

“This external redness was often sexually selected as an ‘honest signal’ of genuine high quality in a mate,” he says.

̽��ֱ��previous research in zebra finches showed a possible link between red beaks and the ability to break down toxins in the body, suggesting external redness signals physiological quality, and there is some evidence that colouration in red-eared terrapins is also linked to honest signalling.

“ ̽��ֱ��excellent red spectrum vision provided by the CYP2J19 gene would help female birds and turtles pick the brightest red males,” says Hanlu Twyman, the PhD student who is lead author on the work.

̽��ֱ��structure of retinas in the eye includes cone-shaped photoreceptor cells. Unlike mammals, avian and turtle retinal cones contain a range of brightly-coloured oil droplets, including green, yellow and red.

These oil droplets function in a similar way to filters on a camera lens. “By filtering the incoming light, the oil droplets lead to greater separation of the range of wavelengths that each cone responds to, creating much better colour sensitivity,” explains Mundy.

“Humans can distinguish between some shades of red such as scarlet and crimson. However, birds and turtles can see a host of intermediate reds between these two shades, for example. Our work suggests that dinosaurs would have also had this ability to see a wide spectrum of redness,” he says.

Over hundreds of millennia of evolution, the CYP2J19 gene was independently deployed to generate the red pigments in the external displays of some bird species and a few turtle species. ̽��ֱ��scientists say their data indicate that co-option of CYP2J19 for red colouration in dinosaurs would also have been possible.

̽��ֱ��ancestral lineage that led to scaly lizards and snakes split from the archosaur line before turtles, and, as the findings suggest, before the origin of the red gene. These reptiles either lack retinal oil droplets, or have yellow and green but not red.

However, the crocodilian lineage split from the archelosaur line after turtles, yet crocodiles appear to have lost the CYP2J19 gene, and have no oil droplets of any colour in their retinal cones.

Mundy says there is some evidence that oil droplets were lost from the retinas of species that were nocturnal for long periods of their genetic past, and that this hypothesis fits for mammals and snakes, and may also be the case with crocodiles.

A gene for red colour vision that originated in the reptile lineage around 250m years ago has resulted in the bright red bird feathers and ‘painted’ turtles we see today, and may be evidence that dinosaurs could see as many shades of red as birds - and perhaps even displayed more red than we might think.

̽��ֱ��excellent red spectrum vision provided by the CYP2J19 gene would help female birds and turtles pick the brightest red males

Hanlu Twyman

Nicole Valenzuela

A Painted Turtle

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Genes discovered that enable birds to produce the colour red

fpjl2 — Fri, 20 May 2016 08:02:04 +0000

Right across the bird and animal kingdoms, the colour red is used for communication, often to attract mates, and zebra finches are no different: the males have a distinctive red beak, which is a sexually selected trait - as females prefer males with redder beaks.

New research on zebra finches has identified for the first time the genes that allow some bird species to produce the red pigment that plays such a critical role in attraction and mating.

̽��ֱ��genes belong to a wider family of genes that also play an important role in detoxification, suggesting how heightened redness may be a sign of mate quality: it indicates a bird's ability to cleanse harmful substances from its body.

This could explain what's known as 'honest signaling': where an evolved trait is a genuine sign of better, fitter genes - in this case the ability to better deal with anything toxic.

̽��ֱ��research is published today in the journal Current Biology.

Birds such as the zebra finch obtain yellow pigments, known as carotenoids, from their diet of seeds, or insects in the case of other bird species.

Prior to the latest findings, it was known that such birds must have a way of converting these yellow dietary pigments into the red pigments - the ketocarotenoids - that colour 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 including Staffan Andersson from the ̽��ֱ�� of Gothenburg and Jessica Stapley from the ̽��ֱ�� 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. In humans, these enzymes are well-studied, as they are strongly associated with drug metabolism.

"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," said Mundy. "Our findings fill this gap and open up many future avenues for research on the evolution and ecology of red coloration in birds."

Red colour 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 colour relates to other beneficial physiological processes, such as detoxification.

"Our results, which link a detoxification gene to carotenoid metabolism, shed new light on this old hypothesis about the honesty of signalling," said co-author Staffan Andersson.

̽��ֱ��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.

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

"It was quite a surprise that the same genes are involved both in seeing red colours and making red coloration," said Mundy.

Mundy says he and his colleagues are now working on the genetics of red coloration in African widowbirds and bishops, which show "spectacular differences among different species."

Latest research suggests a new mechanism for how sexual displays of red beaks and plumage might be ‘honest signals’ of mate quality, as genes that convert yellow dietary pigments into red share cofactors with enzymes that aid detoxification – hinting that redness is a genetic sign of the ability to better metabolise harmful substances.

Our findings open up many future avenues for research on the evolution and ecology of red coloration in birds

Nick Mundy

David Cook

Zebra Finch

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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