Chameleons are definitely one of the most fascinating creatures on Earth, and their characteristic colour changes, to camouflage themselves or gain the attention of their mates, can impress both kids and adults alike. As if their ability to change their appearance into anything they’d like wasn’t enough, the mechanism by which they do so could also be unique and worth some credit.
In nature, colours are usually produced by pigments: substances that have a specific colour. For example, our skin gets tan because of a pigment called melanin which darkens it. In chameleons, it was originally thought that they showed one colour because a pigment of that same colour covered their skin, and when they wanted to change colour, a pigment of a new colour just substituted the original one. But it has now been discovered that their colour change, contrary to popular belief, had nothing to do with pigments. It’s actually all because of crystals.
A chameleon’s skin has an outer layer full of specialised cells called superficial iridophores, which have tiny guanine crystals embedded that can reflect light at different wavelengths and so produce different colours. Guanine not only plays an important role for this process, but is also one of the four bases in our DNA, which code for all the substances in our body. When the chameleon wants to change colour, it simply twist these cells around so the distance between crystals changes, which causes the reflection pattern, and subsequently the colour it produces, to change.
This is a very smart design which saves the chameleons a lot of energy and resources on producing and transporting the pigments around. If the animal wants a bluish colour, it just needs to push all these crystals together. For a reddish/yellow colour, just spread them out.
The only thing yet to be discovered is how the chameleons actually modify the superficial iridophores’ shape. In the experiment they carried out to test this new theory, they used salt water to expand and contract the cells and see what effect this had on the colour. But the natural process in chameleons is not necessarily chemical, it could be mechanical. Finding out which one it is is the team from the University of Geneva’s new objective.
Either way, discovering the truth behind this ingenious technique is not only an interesting fact to know about, but could also have real-life applications, for example, in developing computer screens.