Everyone knows what makes the chameleon so special: its rapid color-changing camouflage. But the bug-eyed lizard's reputation as a master of disguise is being challenged by new research published today in PLoS Biology. Its flexible pigmentation may actually be a sexy, albeit dangerous, way to stick out.
Male chameleons are usually a dull shade of brown or green. But thanks to a special lining of skin cells wired directly to their brains, the lizards can quickly flash to a variety of other colors, including bright green, yellow, and even pink. Past research has shown that the lizards use these colors to intimidate other males when fighting or to impress females when flirting. But the belief persists, even among biologists, that the color change also evolved to help chameleons hide from the birds that hunt them.
To put this idea to bed once and for all, zoologist Devi Stuart-Fox of the University of Melbourne, Australia, and biologist Adnan Moussalli of the University of KwaZulu Natal in Pietermaritzburg, South Africa, studied 21 species of South African dwarf chameleons. Some of these species have a larger color palette than others, using pink, yellow, and even ultraviolet colors invisible to the human eye. The researchers pitted male chameleons against each other and used a spectrometer to measure the range of color patterns that each species produced. They then compared this range of colors to the colors found in each type of chameleon's habitat. The bright hues actually made the lizards stand out, the team reports.
To find out what these colors look like to other chameleons--and to predators--the researchers used computer models that approximated the eyes of various species. They found a clear correlation between a particular chameleon's ability to see and to produce a given set of colors, indirect but strong evidence that the color contrast is meant for "a chameleon's eye view," says Stuart-Fox. But the team also found that birds could see the color contrast pretty well, too, so sporting bright colors is a risky move for the lizards.
The study provides strong evidence that the chameleon's color change evolved mainly for communication, says behavioral ecologist Roger Hanlon of the Marine Biological Laboratory in Woods Hole, Massachusetts. No one has ever shown that the chameleon's special ability provides camouflage, says Hanlon, who reviewed 100 years of scientific literature on the subject. That, combined with the results of this research, he says, should definitively debunk the popular myth--until someone else finds a new species that justifies the belief.