Chameleons' Colorful Flashes Are Social Signals

Jan. 29, 2008 — -- Chameleons are famed for changing color to blend in with their surroundings and hide from predators -- but new research on chameleons in their native habitat shows some of their color changes evolved for exactly the opposite purpose -- attracting attention.

African dwarf chameleons live in habitats in southern Africa ranging from grassland to rainforest.

They engage in complex social signalling, with bright color changes along their flanks used by females to signal interest or rejection to males, and by males to signal aggression or submission to other males, and interest towards females. Males even square off in rapid-fire, colorful signalling duels.

"Chameleons use color change for camouflage and communication, but we don't know why some species change color much more than others," says Devi Stuart-Fox of the University of Melbourne in Australia.

She and colleague Adnan Moussalli reasoned that if these differences evolved solely to enable the chameleon to match itself to its surroundings, chameleons living in backgrounds that vary a lot in color should produce a wider palette, whereas chameleons in less colorful environments should not.

The pair collected males from all 21 genetic groups of dwarf chameleon that live across South Africa and faced them off in duels within their normal habitats. They also measured the colors in their habitats and on the chameleons' flanks.

"We used a spectrometer because unlike humans, chameleons can see in the ultraviolet," says Stuart-Fox. "We wanted to work out how conspicuous a chameleon appeared to another chameleon -- get a 'chameleons eye's view'."

They also assessed how the colors would look to the visual systems of the shrikes and hawks that eat chameleons.

They found that the chameleons' color palette did not broaden with more colorful surroundings, as it would if the driving force on its evolution had been its ability to blend in.

"Species that changed colors the most were the ones with the most conspicuous displays," Stuart-Fox says, meaning the capacity for color change evolved mainly to produce conspicuous social signals.