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Chameleons Evolved Color Changing to Communicate

Anne Casselman
for National Geographic News
January 28, 2008
 
Chameleons evolved their famous skin-altering abilities not for camouflage but to communicate quickly with others, a new study suggests.

Scientists have known that the reptiles use color-changing for a variety of purposes: to blend in to the environment, to regulate their body heat, and to send messages to other chameleons.

Instead of vocalizing or using pheromones, chameleons communicate visually by changing the colors and patterns of their skin. Different colors and patterns mean different things—similar to how the colors of a traffic light direct drivers.

For example, the brighter colors a male displays, the more dominant he is. So male chameleons can attract a mate or defend their territory by flashing bright colors to each other. To communicate submission or surrender, a male will display drab browns and grays.

Females also use a colorful version of signaling to communicate when they want to reject mates or are pregnant.

But how these traits evolved remained a mystery—until now.

Why Bother?

Devi Stuart-Fox, a zoologist at the University of Melbourne in Australia, and her colleague Adnan Moussalli, a biologist at University of KwaZulu Natal in South Africa, ran experiments on 21 species of southern African dwarf chameleons to figure out why these color-changing abilities formed.

(See a photo gallery of colorful chameleons.)

If camouflage drove the evolution of color change, the species of chameleon that display the greatest diversity of skin coloration would have the greatest variety of backgrounds to match their habitats.

One hypothesis is social communication primarily drove the evolution of color change. In that scenario species that possessed the widest range of color change would have the flashiest displays.

So the scientists pitted male chameleons against each other and measured the range of their color change.

"We could use that difference in male dominant and submissive color as a measure of their ability to change color," Stuart-Fox said.

Next they presented the chameleons with a model snake and a stuffed bird to see how well the chameleons could blend into their background when faced with a predator.

"We found that the species that change [the] most are the ones with the most conspicuous displays, whereas there was no relationship between how much they change color and the variety of backgrounds they had to match," she said.

"That suggested to us that it was selection for social communication that was the primary factor driving the evolution of color change in this group," she concluded.

The study appears in this month's PLoS Biology.

Sticking Out

This means that chameleons primarily evolved the ability to change color to stick out to each another—and not to blend in.

"The study is particularly interesting insofar as it helps clarify a common misconception that is in textbooks and [is] widely perceived by the public and scientists alike: that chameleons are masters of camouflage," said Roger Hanlon, a senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts.

"You look at TV commercials and you see changing chameleons," said Hanlon, who was not affiliated with the research.

"Well that's great, but the camouflage changeability story lacks a scientific basis. There's just no meat to that hamburger."

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