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Breaking color barriers.

Kevin McGraw is an assistant professor in evolutionary and systems biology in the School of Life Sciences at Arizona State Univ., Tempe. He heads a group of researchers studying the function and evolution of bird coloration.

McGraw's studies have resulted in major discoveries on the function of the plumage colorings with some implications on the value of appearance for all animal species, including humans. His specific techniques have also resulted in requests from researchers around the world for evaluations of their specific research study samples. "I've analyzed all types of tissues from all types of species from around the world" says McGraw.

As an evolutionary biologist, McGraw initially paid his dues by sitting in hot, tropical jungles catching various songbirds for his research. Now, "with a family, I'm pretty much an urban biologist studying how and why birds have colors," he says.

So what is responsible for the brilliant coloring in birds? McGraw focused his initial research on parrots, which are unusual among birds in their ability to display brilliant colors with little variation between species. It was commonly recognized that the red, orange, and yellow coloring in birds, plants, and fish was chemically tied to biochromes, like cartenoids--a class of natural fat-soluble pigments found in plants, algae, and photosynthetic bacteria. While animals appear to be incapable of synthesizing cartenoids, many incorporate them in their diets.

However, through a complex series of HPLC studies of the red feathers in 44 species of parrots (of more than 350 total species, 80% of which have red plumage), McGraw and co-researcher Mary Nogare found a unique set of five molecules responsible for the red coloring in the feathers, called polyneal lipochromes, or psittacofulvins. The extraction of these tightly bound pigments in the feathers was non-trivial and was mostly responsible for McGraw's successful discoveries.

While McGraw found cartenoids in the bodies of all the parrots, he didn't find them in the feathers. And the lipochromes that he found in the feathers were not found anywhere else in the parrot bodies, implying that they were being manufactured directly at the maturing follicles of the growing plumage.

"The fact that a unique single set of pigments found nowhere else in the world--is widespread among parrots is an evolutionary novelty," says McGraw.

An independent study cited by McGraw suggests that the red pigments in parrots can act as anti-oxidants to quench free radicals and potentially protect cells and tissues within the parrots from oxidative damage--it can make them healthy. So the next logical question posed by McGraw was how the coloring in birds acted on their social behavior. Is the coloring just a function of the bird's health or can it be used as a sexual trait? In this study, McGraw looked at the relationship of coloring in barn swallows.

While most songbirds are traditionally monogamous, it's well known that they typically care for at least one young chick fathered by a bird other than the selected mate. "We found female barn swallows more likely to be faithful to their partners when we experimentally altered their mates' appearance to make his feathers more colorful," says McGraw in a recently published study for Science. This was the first time that female birds were found to make mating decisions based on the changing qualities of their mate.

McGraw's research will now "explore the balance of naturally and sexually selected costs and benefits to becoming colorful" For the time being, however, McGraw will leave any extrapolations of bird coloring to the physical attraction traits in human relationships to other researchers.

Kevin McGraw

Assistant Professor, School of Life Sciences, Arizona State Univ., Tempe PhD, Dept. of Neurobiology and Behavior, Cornell Univ., Ithaca, N.Y. Outstanding New investigator, American Ornithologists' Union/Animal Behavior Society; Post-doc Fellowship, Univ. of California-Davis; Phi Kappa Phi, Auburn Univ.; Phi Beta Kappa, St. Lawrence Univ.
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Title Annotation:study of bird coloration
Author:Studt, Tim
Publication:R & D
Geographic Code:1USA
Date:Feb 1, 2006
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