Scientists have discovered the secret of how chameleons change colour. They do not rely on pigments to create their dazzling hues, but nanocrystals in their skin, which are used to alter the reflection of light.
“We were surprised,” says Michel Milinkovitch, a biologist at the University of Geneva.
“It was thought they were changing colour through… pigments. The real mechanism is totally different and involves a physical process.”
The male lizards use their colour change to impress their mates and to scare away predators.
The discoveries were reported in the journal Nature Communications .
The process of changing colour involves shifting around photonic crystals in a layer of cells just below the chameleon’s pigment cells. Similar cells are found in other reptiles and amphibians like frogs, giving them their bright colours. But In chameleons nanocrystal lattices within the the cells can be “tuned” to change the way light is reflected, say the researchers.
“When the chameleon is calm, the (crystals) are organised into a dense network and reflect the blue wavelengths” of incoming light, they say.
“In contrast, when excited, it loosens its lattice of nanocrystals, which allows the reflection of other colours such as yellows or reds.”
The team used biopsies of chameleon skin, pre- and post-excitement, combined with optical microscopy and high-resolution videography to study the phenomenon.