The chameleon's one-of-a-kind ability to change colors has long been a mystery, but researchers of a new study have revealed that they finally found the secret behind what allows the lizard to change colors in an instant.
The chameleon is not the only animal in the world that can switch colors. Squid and octopus also do, but what makes this lizard different is that it does not modify its hues by dispersing or accumulating pigments in the skin cells. The chameleon instead depends on structural changes that influence how light reflects off its skin.
For the new study published in Nature Communications on March 10, Michel Milinkovitch from the University of Geneva in Switzerland and colleagues wanted to find out how the chameleon changes colors, so they studied a group of panther chameleons, a species that lives in Madagascar.
The researchers found that under the surface of the reptile's skin are iridophore cells that contain nanocrystals of varying shapes, organizations and sizes, and which are responsible for the dramatic color shifts of the chameleon.
The lizards are able to change their colors by stretching or relaxing their skin, which causes the crystal lattice embedded in their skin to change shape, reflect different wavelengths of light and thus in effect change how their color appears.
Milinkovitch explained that when a chameleon's skin is in a relaxed state, the nanocrystals tend to be very close to each other, so the iridophore cells reflect short wavelengths producing the color blue. He added that the crystals are like selective mirrors and that the different colors are produced by the sizes and space of the crystals in the skin.
"Light will bounce on them only for specific wavelengths," Milinkovitch said. "The other wavelengths will not bounce on these cells."
When the chameleon becomes excited, the distance between the neighboring nanocrystals increases, resulting in each of the cells reflecting longer wavelengths such as red, orange or yellow.
The researchers also discovered a deeper layer of skin that reflects near-infrared sunlight, which could help the reptiles regulate their body temperature.
"A deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range," the researchers wrote. "The organization of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection."
Photo: William Warby | Flickr
