Researchers reveal how the chameleon changes colour

The study, which was carried out by a team at the University of Geneva, revealed that photonic crystals cause active colour change in chameleons. Essentially, altering the space between its crystals allows the chameleon to reflect a specific wavelength of light and camouflage themselves.

The study focused on the panther chameleon which is native to Madagascar. When this chameleon encounters 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.

As the study abstract published in Nature Communications notes, by combining microscopy, photometric videography and photonic band-gap modelling, the team shows that chameleons shift colour through ‘active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores’.

In addition, the team, led by Prof Michel Milinkovitch, discovered that ‘a deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range’. According to the study, the organization of iridophores into these two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection.

The Guardian notes that 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. The paper quotes Prof Milinkovitch who said, ‘They’re basically pulling apart or squashing together the lattice.’

It is not clear to scientists 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 study succeeded in busting a popular myth – contrary to popular belief, the idea that chameleons can camouflage against any background isn’t true. Prof Milinkovitch added, ‘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.’