Chameleon skin changes from red to yellow to green faster than a traffic light. The creature’s name has become synonymous with disguise. Most people think these lizards use their color-changing abilities in order to camouflage masterfully. In reality, chameleon color changes are part of complex aggression and mating displays. Until recently, the origin of these color changes was unknown. But in a recent study published in Nature, a group from the University of Geneva revealed that the remarkable chameleon color changes are the result of changing crystal structures within chameleons’ skin.
On a basic level, chameleon skin is colored by groups of cells that contain pigments, just like ours. But while humans—as well as all other mammals and birds—get coloring from cells called melanocytes, which contain melanin pigments, chameleons’ colors come from iridophores. Researchers identified two layers of chameleon iridophores—surface iridophores and deep iridophores—both of which contain nanocrystals made out of guanine. These iridiphores are organized into two layers of lattices. The deep iridophores reflect mostly wavelengths on the infrared spectrum. The surface iridophores are responsible for the visible light color changes that the human eye observes.
So how do these crystals create rapid color change? The secret is not in anything that the iridiphores are able to do themselves, but in something entirely different: the stretching of the chameleon’s skin. As chameleon skin stretches or relaxes, the iridophores embedded in it are pulled into various conformations. The realignment of crystalline structure triggers a change in the color because as the distances between nanocrystals changes, they reflect different colors, changing the appearance of the skin.
Researchers analyzed the skins of panther chameleons using histology to examine cellular anatomy. Transmission electron microscopy helped detail the two-layered crystalline structure of iridophores beneath skin. Color changes were recorded using high-speed videography that allowed close optic analysis. Together these results create a cohesive concept of a nanocrystal lattice that changes color in response to altered skin tightness.
We’re no longer confused as a chameleon in a bag of skittles about the origin of chameleon color. But the precise mechanisms for controlling color change have yet to be determined. For the time being, these creatures remain fascinating examples of the remarkable adaptations produced by evolution.
Sarah Ludwin-Peery is a freshman in Timothy Dwight College. Contact her at firstname.lastname@example.org.
Featured image from here.