Wednesday, May 28, 2008

The Conspicuous Colors Of Chameleons

For years scientist have known that chameleons’ ability to change color served three purposes: camouflage, body heat regulation, and social communication. However, the most widely accepted hypothesis as to what drove this adaptation, up until now, was camouflage, but some recent research has brought new light as to why chameleons have become know as the color changers that they are, and scientist now believe that social communication is the main driver behind this adaptation.

There are more than 160 species of Chameleons known, and their body size and shape varies widely from 1 inch up to 31 inches. Most of them can be found in Africa, Madagascar and other tropical areas. While chameleons have many unique physical features, such as there independently moving eyes and extremely long tongues, their ability to change color has always been the most fascinating.

Photo by sukanto debnath

All chameleons are able to change color, with different species exhibiting different color ranges that include pink, blue, red, orange, green, black, brown and yellow.

Color Change

Chameleons have specialized cells, collectively called chromatophores, that lie in layers under their transparent outer skin. The cells in the upper layer, called xanthophores and erythrophores, contain yellow and red pigments respectively. Below these is another layer of cells called iridophores or guanophores, and they contain the colourless crystalline substance guanine. These reflect, among others, the blue part of incident light. If the upper layer of chromatophores appears mainly yellow, the reflected light becomes green (blue plus yellow). A layer of dark melanin containing melanophores is situated even deeper under the reflective iridophores. The melanophores influence the ‘lightness’ of the reflected light. All these pigment cells can rapidly relocate their pigments, thereby influencing the colour of the chameleon.
- Wiki:Chameleon

Photo by Pashka

The study

Scientists ran experiments on 21 species of southern African dwarf chameleons to figure out why these color-changing abilities formed.

If camouflage drove the evolution of color change, the species of chameleon that display the greatest diversity of skin coloration would have the greatest variety of backgrounds to match their habitats.

Photo by buckoven

One hypothesis is social communication primarily drove the evolution of color change. In that scenario species that possessed the widest range of color change would have the flashiest displays.

So the scientists pitted male chameleons against each other and measured the range of their color change.

The findings

“We could use that difference in male dominant and submissive color as a measure of their ability to change color,” Stuart-Fox said.

“We found that the species that change [the] most are the ones with the most conspicuous displays, whereas there was no relationship between how much they change color and the variety of backgrounds they had to match,” she said.

Photo by Charlotte Hay

“The study is particularly interesting insofar as it helps clarify a common misconception that is in textbooks and [is] widely perceived by the public and scientists alike: that chameleons are masters of camouflage,” said Roger Hanlon, a senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts.

Original here

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