A few years ago, when I was taking pictures of an artificially raised chameleon, Chamaeleo calyptratu, it climbed up to the top of my head along my arm and turned green from a spotted alert.
To give this slightly embarrassing example, the purpose is to tell you that chameleon discoloration is not entirely to adapt to the needs of the external environment. The most important reason chameleons change their body color is that they act as a tool for information exchange, like a silent language, silently expressing joy, anger and sorrow. For example, tall-crowned chameleons show green body color when calm, dense dark spots when nervous, light yellow-green when sleeping, bright yellow or yellowish-brown patches on the side of the body during oestrus, and black-gray when pregnant. It was dotted with dark green and bright yellow markings.
The body color of Furcifer pardalis, the most colorful chameleon, is even influenced by geographical factors. Different body colours are like different identities, corresponding to different origins. Individuals collected from different habitats do not look like the same species at all, although in fact they are not even subspecies, because some groups are not geographically isolated. More interestingly, these chameleons will recognize the different colours of their neighbours and consciously avoid “crossbreeding” with them.
Of course, chameleon discoloration can also be affected by external environment, temperature, physical condition and many other conditions, but these are only secondary factors.
Well, with all that said, there’s a problem. How does chameleon achieve rapid body color change?
It is generally believed that the chameleon has several layers of pigmented cells arranged vertically under its skin, each of which controls a specific color, and is harmonized into different colors through the relaxation and contraction of the pigmented cells, similar to the principle of the TV color picture tube.
But that may be a bit outdated. Last month, researchers at the University of Geneva (UNIGE) in Switzerland presented their view in the Journal Nature Communications that the rapid change in body color was due to the presence of a layer of iridophores on the surface of chameleon dermal cells. The arrangement of guanine nanocrystals in the cell layer allows the chameleon to change its color.
Many kinds of chameleons have gorgeous colors, ranging from red orange to blue and purple, as if all the colors in nature could be found in them – because chameleons have a variety of pigment cells? This is not the case.
The colours displayed by various organisms can be divided into two categories: chemical colours and structural colours. Chemical color is caused by various pigments in organisms, such as melanin, heme, chlorophyll, carotene and so on. It is the real color in organisms. Structural colors, also known as physical colors, are produced by the scattering, interference or diffraction of light at a specific wavelength with certain nanostructures. The rainbows produced by CD-ROMs and some bird feathers are typical structural colors.
Chameleons and other lizards are no exception. The nanocrystals in their rainbow cells are such nanostructures that produce structural colors. When the chameleon is in a calm state, these crystals are arranged tightly, and when light passes, only blue is reflected. The blue structural color combines with the chemical yellow pigment, and the body color is green. When chameleons are tense, they actively control the density of crystals and make them more loosely arranged. Such structures will reflect longer wavelength colors, such as red and yellow light, and thus show more brilliant structural colors. This series of changes can be completed in the blink of an eye.