APR 25, 2014 12:00 AM PDT

The Chameleon, Master of Cell Signaling

The ability to change the color of your skin is like having a super power. If you're an animal living in the wild, there are a lot of good reasons to change your skin color: to hide from predators and prey, to ward off enemies, to establish dominance, and to attract (or repel) a potential mate. Among the animals who can change their skin color, chameleons are the masters of molecular manipulation.

We've all hear the term "social chameleon" in reference to a person that blends into their surroundings. But chameleons don't change color to blend into their environment, they do it to regulate their body temperature and send signals to other chameleons. And if anything, these color changes can make the chameleon more noticeable, not less.

So how do they do it? The skin of a chameleon has layers of specialized cells that contain chromophores. The chromophores are stored in vesicles with pigments that absorb and transmit light at different wavelengths. These include xanthrophores that have yellow color, erythrophores that have a red color, iridiphores that have a blue color, and melanophores that have a brown color.

The chameleon's chromophores change color when specific neurotransmitters or hormones are released as a result of changes in mood, temperature, or stress. When a signal is received, the vesicles discharge, and the color spreads through the cell, altering its color. Differing levels of chromophore activity in different layers of the skin enable the chameleon to display a wide range of colors-like an artist mixing different of colors of paint on a pallet, for example mixing red and yellow chromaphores produces a blue color.

That's why a calm or warm chameleon may be a pale-green color. When it gets cold, it will turn dark brown to absorb more heat. When it gets angry, it might go bright yellow, and when it wants to attract a mate, it will turn every color it possibly can. Some chameleons are capable of producing a kaleidoscope of colors, including of browns, greens, blues, reds, and yellows.

This amazing capability has made chameleons a continuing subject of intense scientific scrutiny for many decades. In one recent experiment published in Biology Letters, Russell Ligon and Kevin McGraw of at the Arizona State University's School of Life Sciences studied the changes in coloring when male chameleons challenged each other for territory or females. They found that in these circumstances, the coloring of male chameleons becomes brighter and more intense. They also found that aggressive males that display brighter colors are more likely to approach their opponent, and those that achieve brighter head colors are more likely to win fights. Even more, the speed at which their heads change color is an important predictor of which chameleon will win.

"Stripes, which are most apparent when chameleons display their bodies laterally to their opponents, predict the likelihood that a chameleon will follow up with an actual approach," said Ligon. "In addition, head coloration-specifically brightness and speed of color change-predicted which was lizard was going to win."

The researchers found that during a contest, the chameleons displayed a show of 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," Ligon said. "The winner is the one that causes its opponent to retreat. While sometimes they do engage in physical combat, these contests are very short -- five to 15 seconds. More often than not, their color displays end the contest before they even get started."

There are approximately 200 species of chameleons in the world. They are omnivorous and live essentially solitary lives except when mating. Many are at great risk due to the rapid destruction of their habitats.

As a point of interest, the roots of the English word "chameleon" have nothing to do with changing color. According to the Miriam Webster dictionary, the word comes from the Greek χαμαιλέων (khamailéōn), which is derived from two other words, χαμαί (khamaí) "on the ground"and λέων (léōn) "lion".
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