Newly-published research suggests the way chameleons change color may be different to previous theories. University of Geneva scientists believe the answer lies in nanocrystals rather than pigment.
The ‘traditional’ theory of how chameleons are able to change color to fit their surroundings was by dispersing pigment in organelles, a ‘subunit’ within cells. In cold-blooded animals, such cells create the color of skin and eyes. A few animals such as squid and octopuses have the ability to control this pigmentation, but it was thought the ability was most pronounced in chameleons.
However, the scientists in Switzerland have been taking a close look at the panther chameleon and concluded that they actually change color by manipulating crystals. These crystals are made from guanine (one of the key ‘ingredients’ of DNA) and are located in a lower layer of skin made up of iridophores. That’s part of the family of cells that make up skin color but, rather than containing a specific pigment, they reflect light.
The Geneva theory is that the chameleon can control the arrangement of these crystals. Normally they are in a lattice structure that mainly reflects blue light, but the chameleon can expand the lattice (pictured) to reflect more yellow or red light. This change shows up as different colors depending on the specific pigment contained in the outer layers.
To replicate this change, the researchers took layers of iridiphores from chameleon skin and forced a change to the crystal lattice by using salt water to draw fluid out. This caused the expected color change.
The researchers aren’t yet clear of the physical mechanism by which the chameleon changes the lattice structure. They are also exploring their finding that the chameleon in fact has two layers of iridiphores. One possible explanation is that one layer is used for changing color, while the other is used to control the reflection of near-infrared light as a way to keep cool.