The secrets of color-changing chameleons revealed
Scientists studying chameleon skin have discovered the secret to the lizards' color-changing prowess: Rather than relying purely on pigments, the animals use photonic nanocrystals in their skin to manipulate light with exquisite precision.
The male panther chameleon (Furcifer pardalis) of Madagascar is an extremely talented shade-shifter. His thick-striped body can go from a blue-green palette to a fiery yellow-red-orange in a matter of minutes, if he wants to show off to an interesting lady lizard or a competing male.
When excited, their skin goes through some very specific color switches, the study authors wrote: Green goes to yellow or orange; blue patches turn whitish; and red becomes brighter and more uniform.
Still, they’re kind of hard to actually find in the wild – their resting color scheme makes for remarkably effective camouflage.
Many scientists assumed that the animals’ speedy shade-shifting came from moving pigments around inside of cells called chromatophores, but Milinkovitch and colleagues doubted that explanation. Pigments – including the ones that we have in our own skin and hair -- typically work by absorbing most colors of visible light except one. So a red pigment absorbs most of the wavelengths of visible light and lets only the red wavelengths bounce off of its surface.
But chameleons also have iridophores, cells that manipulate color in a very different way. Instead of absorbing light, they use a phenomenon known as structural color, which harnesses a surface's nanoscale geometry to force certain wavelengths of light to bend or bounce in specific ways. Structural color is found across the animal kingdom, from the scintillating sapphire wings of the blue morpho butterfly to the iridescent shades of mother of pearl. The scientists identified two layers of skin with iridophores – and the ones in the top layer were filled with tiny nanocrystals of guanine, arranged into lattice formation with very precise spacing between each crystal.