How do chameleons change color? - Paulina Chamely BP7

My first presentation for this quarter was on the Chameleons of Madagascar and the most striking thing that I learned from doing research on these animals was the mechanism by which they change color.

In trying to discover what gave chameleon their green color, they analyzed the pigments in their skin and to their surprise, they noticed that there was in fact no green pigments. In their skin, however chameleons have cells containing yellow, red and some dark melanin pigments. Beneath the yellow pigment cells, there are cells containing tiny 130 nm crystals regularly arranged in a lattice.

Light refracts off of these crystals and due to the spacing, blue light constructively interferes and is therefore strongly reflected while the other colors aren't. So the chameleon looks green due to the combination of the yellow light of the pigment plus the blue light being reflected off the Crystal structure beneath it.

They used this new structural analysis to help understand how they change color. The crystals underneath change and by increasing the spacing of the crystals, the chameleon can choose which color are selectively reflected. Bigger gaps between crystals are better at reflecting longer wavelength so as the spacing increasing, the color changes from blue to green to yellow and then orange and red. They discovered this by comparing the skin of both calm an excited chameleons and compared the differences. In the excited chameleon the crystal spacing was much further apart (as seen below)

As light reflect off of these crystals they begin to move. The more spread out the crystals the different wave lengths they will reflect. This changes the color to which we see on the skin of the chameleon.

 

Interestingly enough they found that this color changing mechanism is not only used as a means of camouflage for the chameleons but is also used as a mechanism of communication among individuals of the species. For example, when female chameleons become pregnant they change amor their usual dull colors to become colorful to inform the males that they are not available to mate with. Another example as displayed in the picture above, a rival male will become more yellow orange and red when excited so that it stands out more to its competitor.