Crystal amaze: how a chameleon changes colour revealed

It is one of nature’s most spectacular displays and now scientists have shown how the chameleon changes colour.

A study has found that the lizards possess a layer of skin cells that contain floating nanocrystals. The tiny crystals are roughly evenly spaced throughout the cell and this spacing determines the wavelength of light that the cells reflect.

The latest research shows that chameleons switch colour from green to red by actively changing the spacing between these tiny cellular crystals.

Prof Michel Milinkovitch and his team at the University of Geneva cracked the problem after years of studying the panther chameleon (Furcifer pardalis), native to Madagascar, which has one of the most impressive colour displays in the chameleon kingdom.

When males encounter a male competitor or a potentially receptive female, it shifts the background colour of its skin from green to yellow, its blue patterning turns white and red becomes brighter.

“This happens within minutes of it seeing another male,” said Milinkovitch.

In the study, published on Tuesday in the journal Nature Communications , the scientists studied the skin of the lizards using spectroscopy. They found that beneath several layers of pigmented skin cells, the chameleons have a layer of cells called iridophores, containing nanocrystals made of guanine, one of the four key components of DNA.

The guanine nanocrystals are arranged in a lattice throughout the cell, the spacing of which determines the cell’s colour. When the chameleon is calm, the crystals were found to be organised into a dense network, reflecting blue wavelengths most strongly. When excited, the chameleon was found to loosen its lattice of nanocrystals by about 30%, allowing the reflection of yellows or reds. “They’re basically pulling apart or squashing together the lattice,” said Milinkovitch.

The scientists are yet to work out how chameleons cause this change, but it could be due to cells shrinking or expanding, giving the crystals more or less space to fill.

The chameleon’s visible colour is also determined by the upper layers of skin cells, which the light is filtered through, containing yellow and red pigment.

Previously scientists had shown that chameleons are also able to change their hue through the migration of melanin in and out of cells, turning them from pale to dark green, for instance.

However, until now it was a mystery how they managed to completely switch colour from green to red in a matter of minutes.

The idea that chameleons can camouflage against any background is a myth, however. “I’m sorry to say this isn’t true,” said Milinkovitch. “Typically they are extremely well camouflaged in their relaxed state, because they are green against a background of leaves, and they are as noticeable as possible when displaying.”