By Dr. Becker
Some animals have evolved to change body color as a way to protect themselves when something changes in their environment. Chameleons, on the other hand, change colors when they interact with other chameleons.
Chameleon Color Changes Serve a Purpose
Researchers at Arizona State University (ASU) have learned chameleon color changes aren't random. They communicate specific types of information during social interactions among chameleons. For example, when a male chameleon challenges another male for territory or a female, his coloring becomes brighter and more intense. And males that exhibit brighter stripes when they are being aggressive are more likely to approach an opponent, and also to win the confrontation.
Another way to determine which chameleon will win is to watch how quickly their heads change color. The fellow with the rapidly changing head color will very likely outlast his opponent.
Chameleon Tough Guys Display Faster Color Changes and Brighter Stripes
In their study, which was published this past December in Biology Letters,1 researchers Russell Ligon and Kevin McGraw of ASU used photographic and mathematical modeling tools in novel ways to observe how the color change of veiled chameleons (Chameleon calyptratus) is associated with aggressive behavior. Ligon and McGraw evaluated the distance, maximum brightness and speed of color change of over two dozen different areas of the chameleons' bodies.
According to Ligon:
"We found that the stripes, which are most apparent when chameleons display their bodies laterally to opponents, predict the likelihood that a chameleon will follow up with an actual approach.
"In addition, head coloration – specifically brightness and speed of color change – predicted which lizard was going to win."
'The winner of a fight is often decided before they actually make physical contact.'
When they are at rest, chameleons typically wear browns and greens, with touches of yellow, but each chameleon is an individual with unique markings. During an altercation, their colors will transform and intensify to bright yellows, oranges, greens and turquoises.
"By using bright color signals and drastically changing their physical appearance, the chameleons' bodies become almost like a billboard – the winner of a fight is often decided before they actually make physical contact," says Ligon. The winner in most cases simply causes his opponent to retreat. When there is actual physical contact, it doesn't last more than 15 seconds. The norm is for color displays to end the contest before it ever gets started.
In this first study of its kind, Ligon and McGraw were able to use information on the physiology and sensitivity of chameleons' photoreceptors to measure the colors actually seen by the lizards.
Many Chameleon Species Are at Risk of Extinction
There are around 160 species of chameleons in the world. Veiled chameleons like the ones observed in the ASU study are native to Yemen and Saudi Arabia. They are omnivorous (they eat both plants and animals), and live alone except when mating. Many chameleons are at risk of extinction due to habitat destruction.