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Boffinry listicle MADNESS: ONE THING you need to know about CHAMELEONS

Crystal-crusted lizard revelations

An inter-disciplinary team of scientists from the University of Geneva has figured out how chameleons manage to exhibit their complex and rapid colour changes by using the crystals in their skin.

"Ever since their description by Aristotle, chameleons have populated myths and legends," says the team of Swiss boffins, evidently keen to prove they'd do as well with University Challenge's classics questions as they would those on biology and physics.

In an article bearing the pleasantly explicit title "Photonic crystals cause active colour change in chameleons" the researchers explain how a combination of "microscopy, photometric videography and photonic band-gap modelling" allowed them to demonstrate, for the first time, how chameleons change their colour for camouflage, communication, and thermoregulation.

While the reptile's remarkable ability to function as a disco light is popularly attributed to some form of pigment-shifting organelles contained in their skin, the Swiss researchers demonstrated how the activity really occurs due to the chameleon's ability to manipulate pigment-containing and light-reflecting cells beneath its skin.

These crystal cells, or iridophores, are present in many other species of lizard: however, they tend to be arranged in one of two ways. The crystals may be arranged uniformly to provide bright colours, or they may be disorganised in order to reflect the heat of their native Sub-Saharan Africa.

Jérémie Teyssier and Suzanne Saenko, co-first authors of the article and physicist and biologist respectively, said:

"We discovered that the animal changes its colors via the active tuning of a lattice of nanocrystals. When the chameleon is calm, the latter are organised into a dense network and reflect the blue wavelengths. In contrast, when excited, it loosens its lattice of nanocrystals, which allows the reflection of other colors, such as yellows or reds".

The study, a collaboration between quantum physicists and evolutionary biologists, revealed that chameleons actually have a double layer of these iridophores, a unique evolutionary invention.

Michel Milinkovitch stated that the second, deeper layer contains "larger and less ordered crystals, [which] reflect a substantial proportion of the infrared wavelengths [providing] an excellent protection against the thermal effects of high exposure to sun radiations in low-latitude regions."

In their future research, the scientists will be exploring the molecular and cellular mechanisms that allow chameleons to control the geometry of this lattice. ®

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