When Does a Chameleon Change Color?
A chameleon will change color when it senses danger. This remarkable member of the lizard family can change color to match its background or, at least, to become almost unrecognizable. The ranges of colors and patterns of the various species differ widely, but most chameleons can become yellow or cream, green or dark brown.
They can also adapt spots either dark or light depending on the color of the ground. Apart from its response to danger, the chameleon will change color according to the light and temperature. This mechanism is controlled from the nervous system and involves the dispersion or concentration of color pigments in the creature’s skin.
However, research conducted in 2014 on panther chameleons has shown that pigment movement only represents part of the story. Chameleons change color by changing the space between the guanine crystals, which changes the wavelength of light reflected off the crystals which changes the color of the skin.
Chameleons have two superimposed layers within their skin that control their color and thermoregulation. The top layer contains a lattice of guanine nanocrystals, and by exciting this lattice the spacing between the nanocrystals can be manipulated, which in turn affects which wavelengths of light are reflected and which are absorbed.
Exciting the lattice increases the distance between the nanocrystals, and the skin reflects longer wavelengths of light. Thus, in a relaxed state the crystals reflect blue and green, but in an excited state the longer wavelengths such as yellow, orange, green, and red are reflected.
The skin of a chameleon also contains some yellow pigments, which combined with the blue reflected by a relaxed crystal lattice results in the characteristic green color which is common of many chameleons in their relaxed state. The deeper layer of skins works in a similar fashion but primarily controls the amount of near-infrared light that is absorbed or reflected, and therefore may influence thermoregulation.
Color change in chameleons has functions in camouflage, but most commonly in social signaling and in reactions to temperature and other conditions. The relative importance of these functions varies with the circumstances, as well as the species.
Color change signals a chameleon’s physiological condition and intentions to other chameleons. Chameleons tend to show brighter colors when displaying aggressively to other chameleons, and darker colors when they submit or “give up”.
Some species, such as Smith’s dwarf chameleon, adjust their colors for camouflage in accordance with the vision of the specific predator species (bird or snake) by which they are being threatened.
The desert-dwelling Namaqua chameleon also uses color change as an aid to thermoregulation, becoming black in the cooler morning to absorb heat more efficiently, then a lighter grey color to reflect light during the heat of the day. It may show both colors at the same time, neatly separated left from right by the spine.