The Mysterious Chameleons
Kolkata, West Bengal
A creature of nature that changes its color. There are thousands of poems and countless metaphors about it! ‘Giridir girgiti môsto bohor’ ('The chameleons in Giridih are exceptionally long.') -Rabindranath, ‘Tiya mukha girgiti mone bhari śôngka’ ('The parrot's face and the chameleon's heart are full of doubt.') -Sukumar Roy. Recent poets have also written many poems. There are many lines about it in English as well.
The chameleon is truly a fascinating creature! It can change its color in an instant. Many people fear this mysterious reptile, thinking it is venomous. Some even close their eyes when they see it.
But why does the chameleon change its color? To survive in the wild, it changes the color of its dense skin. It adopts a form of camouflage. Not exactly a disguise, but it blends into its environment so well that it becomes almost indistinguishable. To predators, it seems like just another part of the environment. Many animals use such natural camouflage to protect themselves by blending in with their surroundings. The chameleon is one such harmless creature. It is not harmful, venomous, or a bloodsucker.
How does it change its color? There are multiple reasons: body temperature regulation, communication with mates, hunting, and confronting enemies, among others. It doesn’t have a natural mechanism to regulate its body temperature in response to environmental changes. Therefore, it adopts a special method to survive.
When the environment becomes hot or cold, humans and animals try to adapt. They manage to a great extent. They use the principles of heat transfer: conduction, convection, radiation, and evaporation. For example, sweating helps keep the body cool during hot weather.
To sustain life, it is essential to regulate body temperature. Otherwise, there is danger! Water inside cells will freeze in extreme cold. Conversely, excessive heat will vaporize the water in the body, leading to death.
The chameleon changes color to regulate its body temperature. In hot weather, it adopts a lighter color, reflecting more sunlight to keep its body cool. In cold weather, it does the opposite, absorbing more sunlight, which makes its body appear brown or khaki.
The chameleon belongs to the lizard family. It lives for five to eight years. Its scientific name is Chamaeleonidae, with the Indian chameleon being named Chamaeleo zeylanicus. There are many species—over two hundred. They are found in many countries in Asia, Africa, and Europe. These animals are called ectotherms. Ecto means external, and therm means heat. They rely on external heat to survive, which is why they change color.
The color change occurs in the skin. But how does it happen? It happens by altering the structure of the cells in the skin. It changes the skin's composition. The altered skin can reflect different colors.
The color of an object depends on the type of light it reflects. An object's color is essentially the reflected light rays.
What colors does the chameleon reflect? In short, many colors. This harmless, astonishing creature can produce various colors. The mystery lies in its skin. The skin is special, consisting of multiple layers (three), and within these layers are pigment cells (chromatophores).
The outer layer of the skin has xanthophores, which create red and yellow colors. The middle layer has iridophores, responsible for blue colors. It is also known as guanophores, named for the guanine crystals it contains. The nano-sized guanine crystals reflect short-wavelength light, producing blue rays.
The third layer contains melanosomes, special cell organelles. They are effective in their function. They can secrete black pigment cells called melanophores. The main role in color change is played by the melanophores. For reference, melanin is found in human skin. It is produced by cells called melanocytes. Melanin protects our skin from many attacks. Melanin is not the same as melanophores.
The melanophores in the chameleon’s skin are star-shaped. They spread across all the layers. When they are dispersed, the skin color appears dark. When they are concentrated in the center, the skin color becomes lighter.
The spread of melanosomes covers a significant area and can obscure other pigments. Depending on the extent of coverage, the skin changes color. The blending of black, red, and yellow pigments can create numerous shades, just like the chameleon does. Moreover, these pigments do not mix and disappear.
The nano-sized pigment particles are contained in small sacs. The different layers of the skin contract and expand, altering the concentration of pigments in various parts of the skin. This creates different colors. Blue and white colors are formed when the guanine crystals in the iridophores reflect or refract light.
It has been said that the chameleon's color change occurs due to temperature changes. The skin has receptor molecules. Receptors sense external temperature and send signals to the central nervous system. Signals come from there, resulting in skin color changes. Genes play a crucial role in this process.
The chameleon’s skin contains two types of iridophores. These cells have an unusual function. Numerous protein plates are arranged within the cells. These act as multilayer reflectors for color reflection.
When in a state of no excitement, the iridophore cells are close to each other, and short-wavelength light is reflected, producing a blue color.
And when the cells are excited, like during an encounter with a predator or when hunting, the distance between the iridophore cells increases, and long-wavelength light (red, orange, yellow) is reflected.
What a wonder! The chameleon can not only change color but also alter its brightness. The male chameleon does this to attract a mate. It is said that this creature changes color for various reasons, including hunting insects, communicating with each other, and scaring off other chameleons.
By sensing external temperature and light, chameleons change their color. Modern research has revealed new insights. A sleeping chameleon in the dark, when exposed to torchlight, suddenly changes its dark-colored body to a lighter shade.
Much has been learned about the chameleon’s color-changing secrets. However, the role of genes in this process remains largely unknown.
The mystery of color change has been uncovered through a century of research. In 1903, Frank Carlton, a zoologist at Harvard University, first reported that the skin of color-changing animals contains a type of pigment cell (Proceedings of the American Academy of Arts and Sciences, Vol. 39, No. 10, Dec. 1903). Extensive research has been conducted since, leading to astonishing discoveries. Recently, Korean scientists have even created color-changing skin (Nature Communications volume 12, Article number: 4658 (2021)).
Could humans ever change colors like chameleons? Possibly. If one could navigate with countless mirrors and optical devices. Recent scientific experiments have made it possible to change colors in plant leaves.
There is still much to learn. Over millions of years, through the process of evolution, chameleons have mastered the art of changing the color of their skin. The skin is the largest organ of the body. It is the first to bear the brunt of external impact. Research on skin is ongoing. Knowledge of color change, the role of genes, etc., could play a significant role in combating many diseases in the future.
Figure 1: The chameleon
Figure 2: The three layers of the chameleon’s skin
Figure 3: Melanosomes, melanophores