Changing colour of a chameleon

SCIENCE FOR YOUTH

BY HIYA ISLAM

science photo

Curled up on a branch in a fine Saturday morning, they are just looking for food: crickets, worms, roaches and what not. They see you, but you don’t. That is how camouflage works. This is what chameleons have mastered over years through evolution. They change colours almost as quickly as some people change their tune these days.

These lizards have a unique anatomy and the best part is the skin that helps them in their color-changing game. For such a special ability comes an elite group of cells called iridophores in the top layer of the skin. They are made up of guanine nanocrystals of different sizes and are arranged orderly.  And now it is just physics in action. When packed densely, these reflect short wavelengths in the blue-green region of the spectrum. But when the cells are pulled apart, they reflect long wavelengths in the red-yellow region. However, chameleons do have pigmented cells. These two features can be combined to produce a variety of colors. Like, yellow cells combined with the blue light reflected off will produce green. Visible light contains 7 colors: red, orange, yellow, green, blue, indigo and violet, all in the order of decreasing wavelength and increasing frequency. The color of an object is the wavelength the body cannot absorb.

There are roughly 200 species of chameleons in the world, most of them found in the super biodiverse land of Madagascar. Some of them like Panther Chameleon, Jackson’s Chameleon, Fisher’s Chameleon can be kept as pets. While their diet consists mainly of creepy-crawlies they are hunted down by snakes, like boomslang, from last week, and birds. One fun fact is that chameleons unlike us can roll their eyeballs in two different directions at the same time!

Changing the skin color helps chameleons in several ways. First of all, camouflage is not even on the list. Research has found that their color depends basically on mood, light intensity and temperature. For instance, when chameleons are hanging out on trees they are relaxed, and their color is green. The nanocrystals are relaxed too, and the reflected blue hue combines with yellow-pigmented cells to give green as already explained. This coincidentally helps them to blend in with the leaves. When threatened or excited, they become red. Lastly, those cells help them to regulate body temperature because reptiles are cold-blooded or ‘ectothermic’. The body temperature of ectotherms depends on that of the surroundings. When the body temperature rises, they change into a lighter color. Again, a cold chameleon will switch to darker shades as they are better heat-absorbers. And as portrayed by cartoons, they do not spend their time matching their body colour with the surrounding environment. They also have absolutely zero interest in changing colors for you even after being your pet.

Surprisingly, only male chameleons are gifted with color-changing abilities. Females and juveniles cannot change their skin color; the number of iridophore cells is too low in those cases.  Then again, don’t only lions have manes? And peacocks have feathers? Not really a surprise, after all.

 

Hiya Islam is a student of Brac University

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