Cephalopod camouflage

Cephalopod camouflage

You have probably seen or heard of an octopus amazingly changing color to blend into its environment. But have you ever wondered how they do this? Scientists are starting to figure out how cephalopods, which include octopus, squid, and cuttlefish, change color. Their skin has three layers. Each has a different type of cell with a different function. The innermost layer of leucophore cells provides a ‘base coat’ by scattering ambient light. The middle layer of skin is made from iridophore cells. These reflect color to provide the blue, green, gold, and silver parts of the animal’s color change. The outermost layer, made from chromatophores, is responsible for most of the color change. Each chromatophore is like a tiny balloon of red, yellow, or brown pigment. When the muscle attached to the chromatophore contracts, it raises the balloon, displaying the color from the pigment. By changing which chromatophores are displayed, the animal can change its skin color. The number of chromatophores in the animal’s skin varies greatly, but some octopus and cuttlefish have over a million. Nerves connect the chromatophores directly to the animal’s brain , so it can change almost instantly. Using the combination of all three layers, the cephalopod can quickly make may different skin colors and patterns.

Scientists still know very little about the molecular mechanisms behind these cells, but they have discovered some interesting information about the iridophores, from the reflective layer of skin. The reflectance comes from certain proteins called reflectins. As Rajesh R. Naik, the lead biotechnology researcher at the Air Force Research Laboratory notes, these proteins are quite unusual because their amino acid sequence is unlike any other known protein. More than half of it comes from four rare amino acids, while four common amino acids are not used at all. Naik’s research team hopes to use what they uncover about cephalopod skin to create new materials, perhaps for camouflage use in the military. They have already created thin films from reflectin that have the highest known index of refraction for a natural protein and can shift color when exposed to certain materials.