ASU researchers discover chameleons use colorful language to communicate

Wednesday, December 11, 2013
by Sandra Leander

To protect themselves, some animals quickly change color when their environments change. But chameleons change colors in strange ways when they are with other chameleons. Arizona State University researchers have discovered that these color changes don’t just happen “out-of-the-blue.” Instead, they display different types of information during important social meetings.

One example is when male chameleons challenge each other for territory or a female. Their coloring becomes brighter and much more intense. Males that display brighter stripes when they are angry are more likely to approach their opponent. Those that have brighter head colors are more likely to win fights. Also, how quickly their heads change color can predict which chameleon will win a battle.

The results of the study are published online today in the journal Biology Letters.

Russell Ligon and Kevin McGraw from ASU’s School of Life Sciences studied the chameleons using photos and mathematical modeling. They used the tools in new ways to study how the color change of veiled chameleons (Chameleon calyptratus) relates to aggressive behavior. They studied the distance, maximum brightness and speed of color change of 28 different patches across the chameleons' bodies.

“We found that the stripes are most obvious when chameleons display their bodies across from their opponents. This predict the likelihood that a chameleon will follow up with an actual approach,” said Ligon. “Also, head coloration – specifically brightness and speed of color change – predicted which lizard was going to win.”

Chameleons typically have resting colors that range from brown to green. There are also hints of yellow. But each chameleon has unique markings. During a contest, the lizards show bright yellows, oranges, greens and turquoises. Sometimes the chameleons showed off their stripes from a distance. Then, they followed that display with a “head-on” approach. Before combat, the important color signals on the striped parts of the body and head were emphasized.

“The chameleons used bright color signals and greatly changed their physical appearance. Their bodies become almost like a billboard. The winner of a fight is often decided before they actually make physical contact,” Ligon said. “The winner is the one that causes its opponent to leave. Sometimes they do engage in physical combat. But these contests are very short – five to 15 seconds. More often than not, their color displays end the contest before they even get started.”

This is the first study of its kind. The research team took pictures of color standards and estimated the sensitivity of different photoreceptors in their cameras. Then, they used information on the physiology and sensitivity of the photoreceptors of chameleons. They were then able to measure the colors actually seen by the lizards. This method has previously been used for unchanging colors. But this study is the first to measure rapid color change with the visual sensitivities of the animals under study.

There are about 160 species of chameleons in the world. Veiled chameleons are native to the Arabian Peninsula – specifically Yemen and Saudi Arabia. They are omnivorous and mostly live alone, except when mating. Many chameleons are at great risk. Their habitats are quickly being destroyed.

The study was funded by an ASU GPSA grant and by individual sponsors.

The School of Life Sciences is an academic unit of ASU’s College of Liberal Arts and Sciences.