Why Can a Chameleon Change Color?

Before knowing more about the chameleon's miraculous ability to change its color, we should know a little more general information about them. The first thing is that there is no one chameleon, but over two hundred individual species under the banner of their scientific name Chamaeleonidae. The true chameleon lives on the continent of Africa, but it can be found in Europe and certain regions of Asia.

It is a relatively solitary animal, usually dwelling on the tree top canopies of jungles without any family group or companions. Only when it is time to find a mate and reproduce does it descend back down to terra firma. In the trees it feeds mainly on insects such as crickets, cockroaches and flies, but will also ingest worms and spiders. They catch their prey in a most unusual method. They can launch their tongue at prey, extending out over twice their body length (excluding tail) and land it on their victim. The insect sticks to the tongue which retracts and enters the Chameleon's mouth for ingestion. The speed at which the lizard does means it takes around 1/10 of a second, giving their prey practically no time for evasion.

This is perhaps an odd question, but the reason for its asking is to distinguish why this lizard and not others. The answer is not really knowable other than it is a quirk of evolution. Some other lizards can change the hue of their color, but none can change so variably as the chameleon.

The standard answer as to why chameleons change color is so that they can camouflage themselves against their environment to evade predators. However, all lizards have predators, yet the chameleon seems so unique. The reasons for their ability to change color and not others stumps scientists, other than the fact they are feats of evolution in many ways. For example, it has recently been discovered that they have twice as many elements in their wrists than before^[1], part of the reason they're so adept at tree dwelling.

With around half the world's chameleon species living on the island of Madagascar, perhaps their concentration required them to adapt in different ways. While we may never quite understand the capriciousness of evolution, we can look at both how chameleons change their color and what other purposes they use it for.

The previously accepted wisdom of how a chameleon changes color was that it was down to special cells in the skin called chromatophores. These contain certain pigments and it was thought the chameleon would change their color by changing these pigment-containing organelles (part of the skin cells). However, this is only part of the story.

A study released in 2014 discovered another aspect of how a chameleon changes its color^[2]. This is down to the layers within the lizard's skin. The top layer contains crystals known as guanine nanocrystals. These crystals move and, in doing so, change the wavelength of the light which passes through them. Some of the light is absorbed by skin and some is reflected off the crystals. This, when combined with the pigment changing organelles, althoughs the lizard to control its color change. This helps to explain why some chameleons can create such a spectrum of color, the crystals breaking up the spectrum of light into its constituent parts.

Now you know how chameleons change color, you may be interested in why they do so. The standard answer is that they do so to camouflage themselves against their environment. However, this answer is too simplistic and the reasons as to why they change color are varied indeed. Let's take a look:

• Protection: only a minority of chameleons ‘actively’ camouflage themselves. This means they adapt rapidly to their surroundings by changing their color and/or markings to resemble their environment. They do this as a response to the vision of their predator, knowing they will be masked. Other chameleons will camouflage in a more basic way, mimicking the color of their surroundings so they they can't be detected by predators scanning the area.
• Temperature: chameleons also change their color according to the temperature of their environment. For example, darker tones are better able to absorb the sun's rays. If a chameleon is too cold, they can make themselves duller to absorb more heat and vice versa. This process is known as thermoregulation.
• Signalling: some chameleons also have florescent capabilities in the form of tubercles which create a ‘window’ into the bone underneath. These bones have florescent properties and can change according to movement of the tubercles^[3]. These tubercles are sexually dimorphic, meaning they change according to the sex of the animal. The implication then is that chameleons use this to signal to the other sex for reproductive purposes. However, male chameleons will also signal to other males when fighting. They show bright colors for confrontation and then dull themselves when they back down.

Actually, a chemeleon will change its color to signal a mood or state of being for many reasons. Next, we will go into more detail as to what these may be.

Although relatively solitary animals, chameleons will still need to communicate with their peers for various reasons. This is a type of non-verbal communication which is very useful in the wild. It includes:

• Stress: in situations of anxiety or nervousness, chameleons will turn darker tones such as black or a range of brown.
• Aggression: during a fight or when they feel threatened by others of the same species, chameleons show a variety of bright colors with red and yellow predominating in many species. This shows they are willing to engage in combat.
• Passivity: if a chameleon is not willing to fight or backs down from an aggressor, they will turn a darker color to show they are not looking for problems.
• Mating: when the female is ready for mating, they will display bright solid colors to the male. Males will usually show a rainbow of color to signal they are ready for mating. The male which shows the greater ability to display their range of color will usually win out.
• Gravidity: when the female has been fertilized, she changes her body to darker colors to signal she is no longer interested in mating.
• Happiness: either from winning a fight or finding some sort of peace against whatever existential problems chameleons might have, chameleons will display bright green tones when they are calm and happy. This is also the tone of dominant males.
• Sadness: conversely, a chameleon defeated in a fight, sick or depressed will display ash, gray or light brown colors.

As we stated before, there are over 200 species of chameleon distributed throughout the world. They do not all change color in the same way. This seems to depend a lot on the environment and the individual species. Neither do all species of chameleon have the ability to display florescence. Some poor species can barely change color at all, instead changing tone rather than full color.

Some species, such as the Parson's chameleon, can only alternate between grey and blue. Others, like the Jackson's chameleon have a range of between 10 and 15 shades.

A third type can only change within the spectrum of black, ochre and brown. They are complex animals which have a fascinating relation to color, our understanding only scratches the surface.

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