Zoology: Chameleons use photonic crystals for camouflage

Chameleons rapidly change colour by actively tuning a lattice of skin cells, reports a study published online in Nature Communications. The study shows that, unlike other creatures, colour changes in chameleons do not rely on the accumulation or dispersion of pigments but on structural changes that affect how the skin reflects light.

The ability to rapidly change colour is vital for chameleons as they use it for camouflage and social interaction. Michel Milinkovitch and colleagues show that chameleons have evolved two superimposed layers of light-reflective cells with different shapes. Chameleons change the structural arrangement of the upper layer of cells by relaxing or exciting the skin, leading to a change in colour, similar to that of active photonic crystal structures. The authors also identified a deeper and thicker layer of skin cells that reflects a substantial portion of sunlight in the near-infrared spectrum and they suggest that the role of this second layer may be that of passive thermal protection.

This study not only sheds light on how pigments and structural changes combine to generate these vibrant colour changes but also poses new questions regarding the evolutionary role of a second deeper layer of infrared reflective cells.