There is a widespread opinion that the chameleon changes its color in order to imitate the environment, as a defense against predators. Those jerks at work, or anywhere, who shift their behavior in accordance to their interests are compared to a chameleon, but this does not happen in the case of the animal. These lizards have evolved their amazing skin-altering abilities not for camouflage, but rather for rapid social communication.
Unlike other lizards that vocalize (geckos) or use pheromones (most of the lizards), chameleons send visual signals by changing their skin colors and patterns. Chameleons have chromatophores (pigment cells), in their skin, containing melanin (which gives the black color) and various other pigments of different colors, but also fat droplets. Chromatophores retire or display their ramifications, and this way the chameleon controls its color.
The color change is under the control of spine nerves and hormones (adrenaline secreted by the adrenal gland and hormones of the hypophysis). Colors displayed by the chameleons vary from gray and black, to whitish, vivid green, green-yellow, olive or blue.
Various colors and patterns encode different messages. Brighter male colors show
off dominance and, this way, a male attracts a female, or defends its territory by flashing bright coloration. Submission or surrender is signaled by drab browns and grays. A female's color signals mating status, willingness or pregnancy state.
Temperature influences the color as well. In the cool mornings, chameleons warm up at the sun, taking a black coat that adsorbs the sun heat easier, besides flattening their flanks. During the night, the chameleons turn whitish, whereas in strong light, they turn brownish. At 25 degrees C, they take on a green color, while at 10 degrees C, their color turns into gray.
If a leaf is put on the back of a chameleon and removed after a period, it will leave a color mark on its back, following its shape, due to the shifts in light and temperature.
A new research published in "PLoS Biology" and carried on 21 species of southern African dwarf chameleons attempted to explain how this color change ability appeared. If camouflage triggered this, the most colorful species would have inhabited the greatest variety of habitats. If the social hypothesis had stood, the species having the widest range of color change would have displayed the flashiest coloration. Male chameleons were put to combat against each other and the range of their color change was assessed. In other experiments, the chameleons were faced to a model snake and a stuffed bird to see how well they camouflage when confronting a predator.
"We found that the species that change [the] most are the ones with the most conspicuous displays, whereas there was no relationship between how much they change color and the variety of backgrounds they had to match. That suggested to us that it was selection for social communication that was the primary factor driving the evolution of color change in this group," said co-author Devi Stuart-Fox, a zoologist at the University of Melbourne, in Australia.
Other researchers have shown that a chameleon attacked by a predator turns reddish with brown or yellow stripes, as most of the chameleons' predators (snakes, mammals) do not distinguish well the colors.
Still, there are some animals that DO copy their environment, like octopuses or many flatfishes (such as flounders), for approaching prey or avoiding predators.
Chameleons rather rely on their ability to stay still for minutes and on their wagging and extremely slow movements (unusual for a lizard) that make their lateral flattened bodies, adorned by spikes, horns and protuberances, resemble a leaf or twig shaken by the wind, in order to pass inconspicuous for their predators and prey.
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