Here’s How Chameleons Change Color
The ability of chameleons to change color has always fascinated us. In most living things, coloration is associated with dead tissues such as the exoskeleton, scales, feathers and hair and is relatively fixed.
Even so, some species are able to change color within minutes. This property allows these animals to display different colors and patterns in response to changing environmental contexts.
Are there any differences between changing colors and changing patterns?
As anticipated, some taxons such as cephalopods, fish and reptiles are able to change their color during interactions with other organisms. Of all these, chameleons (which belong to the Chamaeleonidae family ) represent an intriguing case for scientific research.
Unlike other organisms, which take on a different color in a limited area, chameleons change body colors and patterns during social interactions.
Chameleons change color in response to temperatures
First of all, it is important to point out that chameleons are ectothermic animals. This means that they are unable to generate internal heat themselves. As a result, all ectothermic organisms depend on external heat sources to reach a certain body temperature.
Many characteristics of an ectothermic animal change substantially as a function of the body temperature of the specimen. These characteristics include digestion times, agility in running or swimming, and color, among others.
Remember that dark colors absorb light, and therefore heat, while light colors reflect it. Mimicry is easily understood by anyone who spent a lot of time in a black car under the scorching sun on a summer day.
Chameleons know this and use their skin color as a thermostat to regulate the temperature they receive from the environment.
Change color to impress
The second reason chameleons change color is a concept familiar to humans: self-expression. This is the case of humans who change clothes or hairstyle according to the mood they are experiencing. Even chameleons change color according to their emotions.
Typically, chameleons darken their colors when they are afraid and lighten them when excited. There are also differences between males and females. The former change color more frequently than females, who tend to use more indirect signals to communicate.
In this sense, changing color can also serve the male to attract a possible mate. The bright colors of the male are synonymous with good health in the eyes of the females.
Dark shades, on the other hand, can indicate to another male that you are willing to fight. For all these reasons, a chameleon can adopt different looks every day depending on the situation.
Science investigates chameleon mimicry
In the past, scientists believed that chameleons changed color like octopuses and squid. In other words, they altered their appearance by changing the shape of the pigment sacs contained in cells called skin chromophores. However, chameleons have been found to change color through a much more complex mechanism.
The skin of the chameleon has colors produced by pigments, colored compounds that are synthesized or accumulated in cells. It thus has a range of colors as a result of the action of melanins, pterins and other chemical pigments.
The upper layer of the chameleon’s skin is composed of cells containing pigments: xanthophores if they are yellow, erythrophores if they are red. These pigmented cells are mainly present in the striated areas. The deepest layer is composed of melanophores, with extensions reaching the upper skin layer.
On the other hand, the skin of the chameleon has another type of structural coloration, which is due to the presence of reflective nano-structures.
These nanostructures are present in specialized cells which are called iridophores. They are formed from the guanine content of the cell and produce iridescent metallic colors upon interaction with light.
How do chameleons change color thanks to iridophores?
Iridescence is the optical phenomenon whereby the perceived color is associated with the angle at which the light hits the reflecting surface. That said, it’s easy to understand how chameleon iridophores work.
A recent study reports that the panther chameleon’s skin has two types of iridophores cells. The superficial ones have been called S-iridophores and are found in the layer closest to the epidermis; the deeper ones are called D-iridophores.
In addition to this, each species of chameleon has S-iridophores cells whose guanine crystals differ in size, shape and distribution. The S-iridophore layer is responsible for rapid color changes in the visible light spectrum.
In addition, the guanine crystals in D-iridophores mainly reflect near-infrared light (700–1400 nm). The function of this skin layer is to regulate the temperature when the animal is under intense solar radiation , according to scholars.
Chameleons change color in seconds
It is interesting to know that in the skin of the chameleon which is in a relaxed state, the nanocrystals of the S-iridophores cells are grouped together. In this state, the effective refractive index is optimal for the wavelengths of the blue color.
If the animal is excited, on the other hand, signals are produced that are mediated by hormones or neurotransmitters induced by changes in mood, temperature or stress. As a result, the S-iridophores cells change the arrangement of their nanocrystals.
By increasing the distribution of the nanocrystals, the effective refractive index is lower and the reflectance in the visible spectrum increases for the colors red, orange and yellow.
Ultimately, all of these color production mechanisms are orchestrated to ensure the chameleon the desired look. For example, the color green is the result of the yellow and blue wavelengths. The combination of the yellow of the xanthophores with the light reflected by the iridophores produces the vibrant green color that fascinates us so much.
Final note
It is likely that the chameleon’s dynamic coloring favored the evolution of these complex visual cues. The rich repertoire of chromatic elements of the species reveals the importance of this communication code in social interactions, but also for pursuing other purposes.
