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 identified a thin layer of deformable nanocrystals in their skin which gives rise to 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 -- and hence colour -- related to their spacing. But the researchers have also found that chameleons can change the spacing between crystals. 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.
This is exactly what happens when a male panther chameleon meets a female that it's interested in: its skin shifts from the usual green to a more vivid yellow. The colour does, of course, rely on the upper layers of skin—but it's the crystals that seem to give rise to the rapid shifting of colour. One question does remain though: it's not clear how chameleons bring about the shift in the nanocrystal lattice. 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]
Picture: Riccardo Cuppini/Flickr