Masters of Disguise

A panther chameleon.  Image courtesy of this site.

Chameleons are very special and specialized members of the lizard family.  While the majority, about half of all species, come from Madagascar, they also hail from Africa, Asia, Portugal, and Spain, and Sri Lanka, and they have been introduced to California, Florida and Hawaii.  They are found in warm areas that range from deserts to rain forests.

Side view of a panther chameleon, courtesy of this site.

The very name has an ancient pedigree.  The English word is derived from the Latin chamaeleo, which is a borrowing from the ancient Greek khamailéon (a compound of the words for "on the ground" and "lion"), which in turn is a calque from the Akkadian word meaning "ground lion".

These little guys are courtesy of this site.

They are uniquely built for hunting and climbing, with stereoscopic eyes.  This gives them a 360º view, since their eyes work independently of each other, rotating and focusing separately yet simultaneously.  Their feet are zygodactylous - they have two "toes" facing forward and two facing backward, like many birds. They have prehensile tails and very long tongues which they can stick out very fast, which is fortunate as they can't move their bodies quickly.  These tongues are sometimes longer than their body length, and can hit prey in about 30 thousandths of a second.  At the tip of their elastic tongue is a structure covered in thick mucus which functions like a suction cup.  But most interestingly and uniquely they can change colors.

From G.A. Boulenger, Fauna of British India, 1890.
Image courtesy of Wikipedia.

Only some species can change colors, and different species change different colors.  For a long time it was thought that chameleons change color for camouflage, but now scientists have found that the primary reason for color change is to communicate mood changes to each other, hence functioning as social signaling.  While their basic pattern and color suits their habitat (and it does provide camouflage) light, temperature, and emotions determine their color changes.

Although these Peyrieras' pygmy chameleons are not the smallest, these
ground-dwelling ones are pretty tiny.  Image courtesy of this site.

If a dark chameleon detects a lot of light, its brain tells the yellow cells in its skin to become larger than the blue cells so that it turns green which helps deflect bright sunlight.  If the temperature gets cold, its brain tells it to turn darker so it can absorb more heat.  But mood is the most probably cause for color change.  When a chameleon gets mad it gets dark, which means it's willing to fight.  When it wants to attract a chameleon of the opposite gender, it displays brighter, flashier colors.

A common chameleon, turned black.  Image courtesy of Rickjpelleg/Wikipedia.

Their skin is transparent and they have layers which work together to produce color.  These specialized cells under their transparent outer skin are called chromatophores.  The first layer has two kinds of color cells, yellow and red.  The next layer has cells called iridophores or guanophores, which contain a colorless crystalline substance called guanine, which are strong reflectors of the blue part of light.

Veiled chameleon.  Image courtesy of Geoff/Wikipedia.

Under this layer are melanophores, which have a dark brown pigment called melanin.  This is the same pigment that determines skin color in humans.  The color cells alter the amounts of red, yellow, and brown in the skin.  How much pigment granules are in the cells alter the intensity of a color; if evenly distributed it causes strong color, but if the pigment is only in the center of the cell, it seems to be transparent.  All these cells can rapidly change pigments, and melanin can spread through the cells like a spiderweb.

These are horned leaf or brown leaf chameleons, courtesy of this site.

In an interesting study done in Australia, Smith's dwarf chameleons were watched when they were exposed to two different predators.  When they faced a fiscal shrike, they changed colors to produce the best camouflage.  When a boomslang snake was nearby, they didn't try as hard.  The conclusion was that since snakes have poor color vision, the chameleons didn't waste time and energy trying so hard.

Chameleon faced with shrike.

Chameleon faced with boomslang.

Whenever I see an image of a chameleon, I think immediately of the song "Karma Chameleon" by Boy George.  As it turns out, Boy George is a bit of a chameleon himself.....

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