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Friday, March 13, 2015

How chameleons change their colour?

With a little help from Raman spectroscopy, Swiss scientists have found the answer to an endlessly intriguing evolutionary poser. 

It turns out that chameleons have a mobile “lattice” of#nanocrystals on the surface of their skin, which come together, change shape and disperse thereby shifting the wavelength of light reflected by the reptile.

Scientists studied the panther chameleon Furcifer pardalis from Madagascar, known for its particularly dynamic colour changing abilities — going from green to red within minutes — especially during social interactions such as courtship or male-male combat. These #nanocrystals — of different shapes, sizes and organizations — are distributed in two layers of skin cells called #iridophores (iridescent light-reflecting cells). While the upper layer of iridophores is responsible for rapid colour change achieved by a shift in spacing of nanocrystals in a triangular lattice, the deeper layer of cells broadly reflects light, especially in the near-infrared range, the scientists report in Nature Communications.

The distance between crystals is on average 30 per cent less in the resting state (blue or green skin) than it is in the excited state (yellow or white). With an increase in distance between nanocrystals in excited male panther chameleons, iridophores shift their selective reflectivity from short (blue) to long (red or infrared) wavelengths, causing the corresponding shift from green to yellow/orange skin, says the paper.

Chameleons originated in post-Gondwanan Africa around 90 million years ago. The way these iridophores are organised allows some species “to combine efficient camouflage with spectacular display,” while also potentially providing passive thermal protection.

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