Panther chameleons use nanocrystals to camouflage

Brett Smith for redOrbit.com – @ParkstBrett

Male panther chameleons (Furcifer pardalis) are a wonder of the natural world and during social interactions. They can be seen changing the color of their skin from a pastel pink to neon orange.

Now, a new study published in the journal Nature Communications has revealed these lizards utilize a lattice of nanocrystals contained in a superficial level of dermal cells, called iridophores. The study also found the presence of a deeper group of iridophores with bigger and less organized crystals that reflect infrared light.

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The organization of iridophores into two superimposed tiers points to an evolutionary novelty and it permits the chameleons to quickly change between effective camouflage and a magnificent social display, while offering indirect thermal protection.

Social changers

The study researchers, knowing that panther chameleons camouflage themselves using skin pigments, were particularly interesting in the brilliant social color changes the lizards use as a way to, for example, ward of a rival or show off for a female.

“These colors are generated without pigments, via a physical phenomenon of optical interference. They result from interactions between certain wavelengths and nanoscopic structures, such as tiny crystals present in the skin of the reptiles,” said Michel Milinkovitch, professor of genetics and evolution at the University of Geneva (UNIGE), Switzerland.

In the study, researchers used microscopy, photometric videography and a technique called photonic band-gap modeling to investigate the color-changing aspects of panther chameleon skin. The researchers saw that the nanocrystals within the skin are set up in levels that alternate with cytoplasm, inside cells called iridophores. The entire system allows the animals to selectively reflect certain wavelengths of light, which appear as different colors to our eyes.

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“When the chameleon is calm, the (nanocrystals) are organized into a dense network and reflect the blue wavelengths,” said study authors. “In contrast, when excited, it loosens its lattice of nanocrystals, which allows the reflection of other colors, such as yellows or reds.”

Alas, a second layer!

The study team also discovered a second layer of iridophores underneath the initial layer.

“These cells, which contain larger and less ordered crystals, reflect a substantial proportion of the infrared wavelengths,” which forms an excellent protection against high exposure to sun, Milinkovitch said.

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The study team said they plan to investigate the mechanisms that allow for the development of an ordered nanocrystals lattice within iridophores. They said they also plan to examine the molecular and cellular mechanisms that allow chameleons to manipulate the lattice.

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