The changing colour of a chameleon's body is an impressive sight—but how it happens has long been a significant scientific question without a compelling answer. Now, researchers have finally identified a thin layer of deformable nanocyrstals in their skin which gives rise the phenomenon.
A team of scientists from the University of Geneva has observed that chameleons have a layer of skin cells which contain nanocrystals floating within them. Relatively evenly distributed in the cellular matrix, these crystals reflect light at wavelengths related to their spacing. But the researchers have also found that chameleons can change the spacing between crystals—and it's this that enables them to change colour before our eyes.
By studying the panther chameleon, a team led by Prof Michel Milinkovitch found that beneath the usual layers of skin sits one layer made up of cells called iridophores. These contain the nanocrystals, which are made of guanine—one of the constituents of DNA. The research, published in Nature Communications, reveals that when calm, the crystals reside in a resting lattice shape that mainly reflects blue light. But when agitated, the cells allow the lattice to expand—in turn increasing the reflection of yellow and red light.
Indeed, this is exactly what happens when a male panther chameleon meets a female that it's interested in, as its skin shifts from the usual green to a more vivid yellow. The effect does, of course, rely on the upper layers of skin, which filter the light reflected by the iridophore cells—but it's the crystals that seem to give rise to the rapid shifting of colour. Incidentally, scientists have noticed that chameleons can control the flow of the a pigment called melanin in and out of cells, but that effect is slow than the changing shape of this crystal lattice.
One question does remain, though: it's not clear how chameleons bring about the shift in the nanocystals lattice within their skin. That's the next step for the team—but, for now, at least we known how a chameleon's colours come and go. [Nature Communications via PopSci]
Image by Riccardo Cuppini under Creative Commons license