CAT 2026 Slot 3 VARC Q20: Chameleon Camouflage

Chameleons are oddities within their own extended families. They belong to the class Reptilia and the order Squamata. But they don't resemble their cousins at all. Other squamates include geckos, skinks, iguanas — most are scaled reptiles with a sprawling gait. Chameleons are all crest and tongue, and can be as tiny as 2 centimetres and as large as 25 inches. Some of them have eyes that rotate independently, which is unusual for a reptile. . . .

It makes sense for these reptiles to have added protection in the form of a specialized skin; they don't have a venomous bite, and pretty much everything preys on chameleons, including birds and snakes. But how did chameleons manage to secure their own disappearing act? Chameleons fire from multiple cylinders to achieve this in varying degrees from species to species. There are four main catalysts — melanophores, guanophores, dermal ridges and erythrophores. . . .

[Melanophores] are organs on their bodies that contain pigment sacs, which have black and brown pigment granules. These sacs have a network of radial muscles, meaning muscles arranged in a circle radiating outwards. These are connected to the brain by a nerve. When the chameleon wants to change shade, the brain carries an electrical impulse through the nerve to the muscles that expand outwards, pulling open the sacs to display the shades on the skin. Why these two shades? Because these are the shades the light reflects at the altitudes they live in (the rest is absorbed before it reaches those heights). . . .

Well, what about other colours? Cue the guanophores. Think of a second layer of skin that has thin stacks of crystals. These can reflect light back at different wavelengths. . . . It's using the same properties that we've seen in soap bubbles, or rainbows on puddles of petrol. You move your head and you see a different colour. The bubble isn't doing anything but reflecting light — it's your movement that's changing the appearance of the colour. This property of bubbles, petrol and other such surfaces is called ‘iridescence’. . . .

Dermal ridges are sections of the skin that can be deformed to make a texture spiky. Even humans possess them (goosebumps) but cannot use them in the manner that chameleons can. For instance, the use of these cells is how a chameleon can wrap itself over a branch and appear rough or how a skink or anole can imitate the look of a bark surface by growing miniature bumps on its skin. It actually matches the texture of the substrate it chooses.

Finally, the erythrophores: According to a paper, published in Science, anoles and chameleons possess an additional type of pigment cell called an erythrophore. They are cells that scatter full spectrum light so that they appear red in a similar way that a flamingo's feathers appear pink. Erythrophores will also reflect any filtered light shown on them . . . If the forest appears green at a certain altitude, the anoles and chameleons can appear green; if the forest appears brown, they appear brown, and so on and so forth.