Why Do Chameleons Change Color?
Changing color in animals is a process that has always left us amazed. In most living things, coloration is associated with dead tissue, such as exoskeletons, scales, feathers, and hair, and is relatively fixed. Still, some species are able to change color quickly. This property allows them to display different colors and patterns in response to changing environmental contexts.
Is there a difference between color change and pattern change?
As mentioned earlier, some taxa, such as cephalopods, fish and reptiles, have the ability to change color during interactions with other organisms.
Among all of them, chameleons (family Chamaeleonidae) represent an intriguing case for researchers. Unlike organisms that may have a change of localized color, the chameleons can change the colors and body patterns during social interactions.
The chameleon changes color in response to temperature
First, it is important to note that chameleons are ectothermic animals. In other words, they are not able to generate internal body heat on their own. For this reason, all ectothermic organisms depend on external heat sources to reach a certain body temperature.
It is important to keep in mind that many of the characteristics expressed by an ectothermic animal change substantially according to the individual’s body temperature. These traits include digestion speed, agility when running or swimming, and coloring, among others.
That said, we should consider that dark colors absorb light and therefore heat, while light colors reflect it. Therefore, the color change strategy is something easy to understand for anyone who, on a summer day, spent hours in a black car in the blazing sun.
Chameleons know this and use their skin color as a thermostat to control the temperature they receive from the environment.
Dress to impress: the color change strategy
The second reason chameleons change color is also a concept familiar to humans: self-expression. This is what happens to humans when we change our clothes or hairstyles to suit our mood. Chameleons also change color according to their mood.
The chameleon usually darkens its colors when it’s scared and makes them lighter when it’s excited. Furthermore, there is a difference between males and females: the male change color more often than females, which often use more subtle signals to communicate.
In this sense, changing the color of male chameleons can be helpful in attracting a mate. By displaying strong tones, they send a signal of a healthy state to females. On the other hand, switching to dark tones can show another male that they are willing to fight. For these reasons, a chameleon can switch between several different colors each day to suit the occasion.
The science behind the magic of color change
Scientists once believed that chameleons change color in a similar way to octopuses and squid. That is, to alter their appearance, they would use pigment-filled bags in cells called chromophores. However, it has been found that the chameleon’s color change is even more complex.
The chameleon’s skin has colors produced by pigments, colored compounds that are synthesized or accumulated in cells. Thus, there are a variety of colors that result from the presence of melanins, pterins and other chemical pigments.
The top layer of the chameleon’s skin is composed of cells that contain pigments : if they are yellow, they will be xanthophores; if they are red, erythrophores. These pigmented cells are mainly present in striped regions. The deepest layer is composed of melanophores, which have extensions that reach the top layer of skin.
On the other hand, the chameleon’s skin also has another type of structural coloration that is due to the presence of reflective nanostructures. These nanostructures are present in specialized cells called iridophores. They are produced from the cell’s guanine content and produce iridescent metallic colors when interacting with light.
How do iridophores work to make color changes happen?
It is important to highlight that iridescence is the optical phenomenon through which the perceived color is associated with the angle at which light strikes the reflecting surface. That said, we can understand how the chameleon’s iridophores work.
A recent study determined that the skin of the panther chameleon has two types of iridophore cells: the superficial, which were called S-iridophores, located in the closest layer of the epidermis, and the D-iridophores, in a deeper layer.
In addition, each species of chameleon has S-iridophore cells with guanine crystals of different sizes, shapes and distributions. This layer of S-iridophores is responsible for the rapid color changes in the visible light spectrum.
In addition, crystals in D-iridophores primarily reflect near infrared light (700-1400 nm). Thus, the researchers point out that the function of the D-iridophores layer is to regulate the temperature when the animal is under intense solar radiation.
How does the chameleon manage to change color so quickly?
Interestingly, in the skin of a chameleon in a relaxed state, the nanocrystals in the S-iridophore cells are clustered close together. In this state, the effective refractive index is ideal for blue wavelengths.
On the other hand, in a state of excitement, signals mediated by hormones or neurotransmitters are generated, induced by changes in mood, temperature or stress. In response, the S-iridophore cells alter the arrangement of the nanocrystals. In this way, as its distribution is spaced, the effective refractive index becomes smaller and the reflectivity in the visible spectrum increases for the colors red, orange and yellow.
Finally, all of these color-producing mechanisms are orchestrated to give the chameleon its appearance. For example, the green color of your skin is the result of yellow and blue wavelengths. The combination of the yellow of the xanthophores, together with the blue light reflected by the iridophores, produces the vibrant green color that makes us wonder.
Final grade
It is likely that the chameleon’s dynamic coloration has driven the evolution of these complex visual signals. The species’ rich repertoire of chromatic elements reveals the importance of this communication code for their social interactions and for other behavioral contexts.
