Research Stories

by Skip Derra

Mom always said, "Eat your veggies and good things will happen. She may have been right all along, according to the results from a new study of zebra finches at Arizona State University.

Kevin McGraw is an assistant professor in the School of Life Sciences. He delves into the nuances of the bird world. During his research with birds, McGraw found that carotenoids have even deeper health benefits than originally thought.

Carotenoids are the pigments that color carrots orange and corn yellow. The ASU scientist says that they appear to fight off the negative impacts that testosterone can have on an animal's health.

McGraw worked with Daniel Ardia, a biologist at Franklin and Marshall College in Pennsylvania. Their work focused on zebra finches, a common domesticated pet bird originally from Australia.

Carotenoids are known to play several key roles in birds and fish, including contributing to their bright colors, which act as a signal to attract potential mates. They also act as an antioxidant in the body, which improves immune system function.

A male zebra finch (left) and female zebra finch (right)

McGraw says that researchers in animal behavior often study what keeps sexual signals like bright colors or elaborate songs ‘honest.' Why is it that all individuals cannot produce them ad nauseam and try to get mates?

The reason is fairly simple. "Long tails and fancy dances incur costs," McGraw says. "Testosterone, for example, has been thought of as a double-edged sword as it relates to sexual signals. It enhances trait production but comes at a health price to the animal."

The results of McGraw and Ardia's work show that testosterone may not be as costly as previously thought, so long as animals can nutritionally offset the immune detriments of testosterone.

"They may even experience a net health benefit as a result," McGraw explains. The ASU scientist studies the functions of naturally occurring chemicals in birds and their relationship to the birds' colors and health.

"In the case of the zebra finch, the cost is in the pigments," he says. "The bird must have enough of them to develop a red beak and enough to combat testosterone, which it also needs to be red."

McGraw and Ardia describe their findings in "Do carotenoids buffer testosterone-induced immunosupression? An experimental test in a colorful songbird," in the June 6, 2007 issue of Biology Letters, a journal of the Royal Society in London.

The ASU biologist says that their findings show that there are nutrient-specific mechanisms by which animals can avoid the immune costs of testosterone elevation and still keep their attractive and bright colors. Most previous studies of this sort have focused on physiological or even genetic links between testosterone and health. He adds that it is worth considering the implications for human nutrition and health.

"If testosterone is having immunosuppressive effects in human men, perhaps they too could benefit from increased carotenoid intake, say, by eating more corn," McGraw says.

"This study certainly opens the door for future work on nutritional/antioxidant therapy for the hormonally immunocompromised," he adds. "The interface between diet and health in animals is a fascinating one. But we need a much better understanding of their interactions, as with testosterone, at the molecular level."

Listen to an interview with McGraw: http://sols.asu.edu/podcasts/index.php#vol_12