May 25, 2018 | Updated: 09:54 AM EDT

What are ‘Iridophores’ and How Are They Keeping Chameleons Camouflaged?

Mar 11, 2015 02:13 PM EDT

In a new study published this week in journal Nature Communications, researchers with the University of Geneva in Switzerland revealed that crystals beneath the skin of chameleons are responsible for the species' amazing ability to adapt its pigmentation to its surroundings. But many are left wondering-what exactly are "Iridophores" and how can chameleons use them to camouflage?

Beneath the epidermal layer of skin that protects chameleons, the lizard species has different layers of cells below that help give them their unique pigmentation. But amongst these layers also lie tiny crystals that allow their color-changing ability to take shape. Known as "iridophores", the subsurface crystals are key to a chameleon's color.

In basic terms the researchers of the new study explain that the tiny iridescent crystals allow chameleons to act like selective mirrors, choosing which colors they reflect and which colors they absorb.

"Light will bounce on them only for specific wavelengths" coauthor of the study, Michel Milinkovitch says. "The other wavelengths will not bounce on these cells."

However, past studies into the origins and functions of iridophores have proved their functions to be far more complex and difficult to interpret. In the study of cephalopods and zebra fish, both of which also possess these color-bending abilities, researchers have found that rather than melanocytes that they'd expect to find in mammals and birds, pigment molecules known as chromatophores tend to be found in other phyla across the animal kingom-iridophore being an important one associated with camouflage.

"Color patterns are prominent features of many animals; they have important functions in protection against UV irradiation, camouflage, kin recognition, shoaling and sexual selection" lead researcher of an associated study recently published in the journal Development, Hans Georg Frohnhöfer says. "Color patterns in birds and mammals are generated by melanocytes, which produce melanin and transfer it to the tissues of fur or plumage. In fish, amphibia and reptiles, chromatophores retain their pigment and it is their distribution in the dermis that determines the pattern."

Unlike normal chromatophores that merely absorb or reflect certain regions of the visible spectrum of light, giving them distinct colors, researchers believe that iridophores have the ability to absorb or reflect any and all colors of the spectrum. In the example of the zebra fish, they are in fact exactly how the species is able to change its stripes.

But how are chameleons able to camouflage their entire bodies?

While the process is evidently not nearly as quick as with cephalopods, who can change the texture of the skin and their coloration with the blink of an eye, it appears that chameleons are able to change their color by moving the crystals around beneath their skin. And if they need a really drastic change, with the approach of a competitor or a predator, the researchers found that chameleons are also able to shed their outer layers of skin to expose the iridophores directly to sunlight, giving them a more effective punch of color.

"It's a real social display" Milinkovitch says. "It really demonstrates that the color change is happening due to the modification of these crystals."

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