In a study described in the Nature Communications journal, scientists have found out the secret to the color-changing ability of chameleons: the use of photonic nanocrystals in their skin to control light, Los Angeles Times earlier reported.
Madagascar's Furcifer pardalis or the male panther chameleon, for example, is a color-shifter that can change hues in just a matter of minutes. From blue-green to a yellow-red-orange palette, it can quickly shift its body color when excited, e.g. showing off to a competing male or a lady lizard.
Due to this ability, the male panther chameleon is very difficult to find in the wild, as its camouflaging ability is remarkable.
"I assure you: In Madagascar, they are really difficult to spot," cited co-author Michel Milinkovitch.
The scientists were fascinated with the ability of chameleons to change skin color with exquisite precision, but also admitted that it was not that easy to study the reptiles. Milinkovitch said they are difficult to raise in captivity, with eggs taking a long time to incubate.
Some scientists previously assumed that the reason why chameleons can shift their skin color so quickly is due to chromatophores, the moving pigments in cells. Milinkovitch and his colleagues had doubts with this assumption. After all, pigments function by absorbing most of the hues of visible light.
But apart from the chromatophores, chameleons also possess iridophores, cells that control color by using the structural color phenomenon.
In the study, the scientists used different methods, which included filming the shade shifting with the use of photometric videography, analyzing the nanoscale structure of a chameleon's skin through transmission electron microscopy.
They found out two layers of skin bearing iridophores, with the top layer full of nanocrystals. These nanocrystals were in a lattice formation, with a spacing in between. The researchers said that the "spacing" was the key, as the crystals space further apart when male chameleons show off or get excited.
"When the skin is in the relaxed state, the nanocrystals in the iridophore cells are very close to each other - hence, the cells specifically reflect short wavelengths, such as blue," Milinkovitch said in a report by LiveScience.
The second layer acts as a reflector of infrared light, which is a survival mechanism for animals living in hot, dry places, the researchers added.