Colors tell chameleons' many moods

Dear Dr. Universe,

How do chameleons change color?

Andrew Uehling, Nebraska

Well, everything I thought I knew about chameleons was wrong. I talked with Erin Kelso, a graduate student in zoology here at Washington State University. She studies mating behavior in the veiled, or (because they are from Yemen) Yemenese chameleon.

First, I learned that while chameleons do change colors, they do not change colors in order to blend in with their backgrounds.

Yemenese chameleons are mostly green and yellow. Some are more orange. I know that sounds pretty conspicuous, but because of patterns on their bodies, they're well-camouflaged, no matter what color they change.

Every color pattern a chameleon wears is hard to spot against the trees and brush where it lives because it has dots and stripes that break up the body outline.

So if they don't need the change to blend in, why do they change color?

For one thing, they will turn darker if they're cold and want to soak up some sunlight. But mostly, says Kelso, they change color according to their mood. Much of this mood shift has to do with mating behavior.

When I visited her lab, Kelso put a male chameleon in a cage with a female to demonstrate. First thing the female did was turn dark. Then she attacked the male! Definitely not in the mood.

Kelso rescued the poor guy, who by then was pretty dark himself. She explained that when he's happy and comfortable and sure of himself, he'll turn really light. But because he was worried and caught out in the open and not in a good mood, he was dark.

Male chameleons seem to have a pretty short attention span, however. When they've forgotten how the females attack them, they turn very bright and flatten out to make themselves look bigger, trying to attract the female's attention.

Like many reptiles, chameleons are visual animals, says Kelso. Chameleon eyes are truly bizarre. They protrude on either side of their heads. Each eye has a 180-degree field of vision. This extremely wide angle of vision means a chameleon can sit motionless and see all around it, keeping an eye on predators, or prey.

Their unusual eyes also give them excellent eye-tongue coordination. When they spot something good to eat, their eyes point forward, giving them stereo vision (like yours) and depth perception. This is important because, as you may know, they catch their food with their long, long tongues.

Kelso took out a container of meal worms and held one in the cage opening of a female. Her eyes targeted in on the worm and WHAP! Faster than you can snap your fingers, her tongue whipped out and the meal worm disappeared into her mouth.

But back to how they change color.

Chameleons have special cells called chromatophores. "Chroma" means "color." "Phore" means "carrier." These color carriers, of various colors, lie in distinct layers.

The deepest layer holds the brown-black pigment melanin, which is the same pigment that makes up human sun tans.

Melanin cells have branches that reach up into the upper skin layers. When a chameleon is feeling stressed or in a bad mood, it sends melanin into the upper layers, darkening them.

In addition, the other color cells expand and contract like little balloons, leading to the change in color.

So why did Kelso choose to study mating behavior in the Yemenese chameleon? It's a great case of hobby becoming science.

Her aunt raises chameleons, and she started raising them herself when she was in high school. When she became interested in graduate research in animal behavior, she figured why not study her chameleons?

Have a question? Send Dr. Universe an e-mail message: AskDrUniverse@wsu.edu. Or write to her: Dr. W.S. Universe, Washington State University, Pullman, WA 99164-1040. Or visit her Web site: www.wsu.edu/DrUniverse/. Ask Dr. Universe is a service of Washington State University.