Milinkovitch’s lab, in collaboration with the Quantum Materials Group (Dirk van der Marel, University of Geneva), has demonstrated that chameleons sport two superimposed layers of iridophores – non-pigment cells full of guanine nanocrystals – of a different nature; an evolutionary novelty.
The first iridophore layer is thick, close to the surface of the reptile’s skin and full of nano-crystals neatly arranged in a triangular lattice. The second layer is situated deeper down in the dermis and full of larger and more disorganized nano-crystals. Colour changes on the chameleons’ skin are caused by active tuning of the lattice within the superficial layer of iridophores, while the deeper layer reflects a large proportion of the sunlight radiation energy, especially in the near infrared.
So chameleons are consequently equipped with an amazing toolkit: two layers of iridophores with different morphologies and functions – the first is involved in camouflage and social interactions, whereas the second protects the animal against overheating.
Article (Teyssier, J. et al. Photonic crystals cause active colour change in chameleons. Nat. Commun. 6:6368 doi: 10.1038/ncomms7368 (2015)) and videos here