Do orange lizards wish they were blue?

Male tree lizards, Urosaurus ornatus, come in two colors. Some have an orange flap of skin, called a throat fan, under their chin (left); others display an orange throat fan with a blue or green spot (right). "The blue is a status signal," says graduate student Rosemary Knapp of Arizona State University in Tempe. The bigger the blue area, the greater the likelihood that its bearer will win a dispute with another male.

Even tethered, a blue bigwig stakes out a territory and will defend females within it against other courting males (lower right). Orange males either roam, seemingly aimlessly, or stick near one territory and act as if it's theirs whenever the blue male goes elsewhere.

Michael C. Moore, Knapp's adviser, and his team first found that status was in part genetically determined but could be manipulated by giving hormones to young lizards right after they hatch. Surprisingly, concentrations of testosterone (which helps make an animal aggressive) and corticosterone (which imparts submissive behavior) in the lizards' blood appear about equal in both high- and low-status individuals, Knapp says.

After a fight, the amount of corticosterone increases in orange males but stays the same in blues, even when those animals lose, Knapp reported this week in Miami at the annual meeting of the Society for Neuroscience.

She measured concentrations of the hormones in the blood of 40 lizards, then marked and released nine orange males in the desert. A month later, whenever she found a marked male, she tied a blue male nearby. After the orange male fought off the blue one, she tracked the amount of corticosterone in the marked male for a week.

The hormone didn't increase until 1 day after the fight, and it returned to normal within 7 days. "This really delayed effect is unprecedented," Knapp says.

She thinks that because corticosterone aids the metabolism of carbohydrates, its rise helps the orange male overcome exhaustion from fighting. During that recovery time, the male seems to wander more and be more submissive, perhaps to avoid getting into another fight.

"[The hormone] really does seem to influence a whole suite of behaviors," she adds. Therefore, she and Moore expect that the more an orange male fights, the more nomadic he will be.