Nature blessed chameleons with incredible powers of camouflage, as well as the ability to turn bright colors on command. New research shows that they possess an elaborate array of tiny crystals beneath their skin that they can physically shift about to change their appearance.
Researcher Michel Milinkovitch and colleagues from the University of Geneva performed an in-depth analysis of live panther chameleons (Furcifer pardalis) to try to learn how males can quickly turn bright shades of orange and yellow. Their findings were described in a study published in the journal Nature Communications this week.
The scientists found that usually, when the animal is in a relaxed mood, the special optical crystals in the animals’ skin are close together, in such a configuration that they reflect blue light. But the animals don’t look blue—they look green. That’s because “the skin also contains yellow pigments,” Milinkovitch says. The yellow pigments plus the blue-reflecting crystals make the animal appear green. “This is a cryptic color, and the animal is very difficult to spot in a tree,” he says.
The cells in which these nanocrystals are found, called iridophores, swell when the animals get excited. This causes the crystals to become spaced further apart, a configuration that leads them to “reflect longer wavelengths [of light], such as yellow, orange or red,” Milinkovitch says. Only mature males can change color, he says, and they do so when they see another chameleon male or a potentially receptive female, for the twin purposes of intimidation or attraction.
Beneath these iridophores, the chameleons also have other layers of pigments that reflect infrared radiation, or heat, which helps to keep them cool in the hot jungles of Madagascar where they live.
The dual-layered system “allows these lizards to combine efficient camouflage with spectacular display, while providing passive thermal protection,” he says. “Nice tool kit, if you ask me.”
A better understanding of the chameleon’s trick could help engineers who are trying to make color-changing materials for camouflage. “These living organisms have been doing that very well for hundreds of millions of years,” Milinkovitch says.