Chameleons Use Built-In Crystals to Change Color

Color-changing panther chameleons are among the most disco-ready lizards, courtesy of tiny, built-in crystals that rapidly create multicolored hues. 

Embedded in the panther chameleon’s skin are not one, but two layers of crystal-containing cells, scientists at Switzerland’s University of Geneva report Tuesday in Nature Communications. Stretching or relaxing the cells helps the animals rapidly change color by changing the color of reflected light. (See more amazing chameleon pictures.)

Only adult male panther chameleons (Furcifer pardalis) have a fully developed upper layer of the cells, called iridophores, which they use to put on multihued shows for mating. When the crystals are close together, such as when the animal is relaxed, they reflect blue light. When they are combined with yellow pigments in the chameleon skin, the animal appears green. Stretching the cells and moving the crystals farther apart produces colors ranging from yellow to red.

All of the chameleons have a deeper layer of iridophores that reflects a broader spectrum of light, particularly the near-infrared, which is invisible but is close to the wavelengths felt as heat.

Scientists speculate that these deeper crystal-containing cells help the cold-blooded animals regulate their body temperature, while the more superficial layer of color-changing cells is involved in camouflage and flashy mating displays. (See photos of insect masters of camouflage.)

Why It Matters

The new study is the first to find two layers of crystal-containing cells in chameleons, each with a potentially different purpose.

The different uses suggest that chameleons evolved a double, or even triple, duty for the crystals: efficient camouflage along with spectacular displays and protection from extreme sunlight exposure, says Michel Milinkovitch, one of the study authors.

The Big Picture

In nature, there are essentially two ways to make something colorful: using pigments, or having a matrix of crystal structures that reflects light. Called photonic crystals, these light reflectors are responsible for the colorful shimmer on butterfly wings, beetles, fish scales, and feathers. (Find out what makes butterflies so colorful.)

They also help cephalopods—the ultimate masters of camouflage—blend into their undersea environment. (See more photos of undersea camouflage.)

Pigments can fade, but structural color retains its sheen until the underlying crystals are destroyed.

What's Next

Milinkovitch and colleagues note that although they’ve been able to demonstrate that chameleons can tune these crystal-containing cells, they still don’t know exactly how they do it.

While they figure out how chameleons control their crystals, other scientists are mimicking natural color-generating nanoarchitectures in the laboratory to produce materials such as paints and fabrics with everlasting color.