In a new study published in the journal Nature Communications, Swiss researchers demonstrated that these changes take place via the active tuning of a lattice of nanocrystals present in a superficial layer of iridophores.
Researchers found the results by studying the panther chameleon, from Madagascar. They found tah that the chameleon actively controls how the cells are arranged, and what colour it will be.
The scientists also reveal the existence of a deeper population of iridophores with larger and less ordered crystals that reflect the infrared light.
The organization of iridophores into two superimposed layers constitutes an evolutionary novelty and it allows the chameleons to rapidly shift between efficient camouflage and spectacular display, while providing passive thermal protection.
“Besides brown, red and yellow pigments, chameleons display so-called structural colors,” said study senior author Prof Michel Milinkovitch from the University of Geneva’s Department of Genetics and Evolution.
“These colors are generated without pigments, via a physical phenomenon of optical interference. They result from interactions between certain wavelengths and nanostructures, such as tiny crystals present in the skin of the reptiles. These crystals are arranged in layers that alternate with cytoplasm, within iridophores.”
“The structure thus formed allows a selective reflection of certain wavelengths, which contributes to the vivid colors of numerous reptiles.”
To determine how the transition from one flashy color to another one is carried out in the panther chameleon, Prof Milinkovitch and his colleagues used their expertise in both quantum physics and in evolutionary biology.
“We discovered that the animal changes its colors via the active tuning of a lattice of nanocrystals,” said co-authors Dr Jérémie Teyssier and Dr Suzanne Saenko.
“When the chameleon is calm, the latter are organized into a dense network and reflect the blue wavelengths.”
“In contrast, when excited, it loosens its lattice of nanocrystals, which allows the reflection of other colors, such as yellows or reds.”
“This constitutes a unique example of an auto-organized intracellular optical system controlled by the chameleon,” they said.