Many chameleons have the remarkable ability to make rapid and complex color changes in their social interactions. In a collaboration between biology sections researchers and physics at the Faculty of Science of the University of Geneva (UNIGE) results in the discovery of the mechanisms governing the phenomenon. In the study published by Nature Communications, the group co-led by Professors Michel Milinkovitch and Dirk van der Marel demonstrates that the changes occur through the active control of a nano-crystal mesh present in a surface layer of skin cells, the iridophores. The researchers also testify to the existence of a deeper layer of iridophores, whose crystals, bigger and less organized, reflect infrared light. Such a superposition of two different types of iridophores is new in evolutionary terms; it is what allows chameleons spend an effective camouflage a spectacular parade in record time; is that it also provides a passive thermal protection to the animal.
The colorful adornments that turn at the discretion of the popularity of behavior are male chameleon. While the mechanisms of change to a darker hue are known, those that govern the transition from a bright color to another flamboyant tone remained mysterious. Some species, such as the panther chameleon, for example, are able to make such a transition in one to two minutes, to woo a female or face another male.
The blue color of the chameleon structural
Besides brown pigments, red and yellow, chameleons and other reptiles have called structural colors. “These colors are actually created without pigments, via an optical interference phenomenon. They derive from interactions between certain wavelengths and nanoscopic structures such as tiny crystals in the skin of reptiles, “says Michel Milinkovitch, professor at the Department of Genetics and Evolution of the University of Geneva.These nanocrystals are arranged in alternate layers with the cytoplasm in iridophores named cells. Millefeuille formed selectively reflects certain wavelengths and this phenomenon contributes to the flamboyant colors many reptiles.
To determine how is the transition from a colorful adornment to another in the panther chameleon, researchers from two laboratories of the University of Geneva have worked hand in hand, combining the skills of experts in quantum physics and biology of evolution. “We found that the animal can change color by active adjustment of nanocrystals mesh. When the chameleon is calm, they are organized into dense network and reflect the lengths of blue waves. But the excitement causes release within iridophores of the animal and allows reflection of other colors, such as yellow or red “explain Jeremiah Teyssier physicist and biologist Suzanne Saenko, who are the co-first authors of the article. The set is a unique example of self-organized optical system controlled by the animal wearing it.
Crystals as heat shield
Scientists have also demonstrated the existence of a second layer of iridophores, deeper. “These cells, which contain larger crystals and less organized, reflect a significant proportion of infrared wavelengths,” explains Michel Milinkovitch. This layer acts as a very effective protection against thermal effects due to exposure to the sun in low latitudes.
Furthermore, in terms of evolution, the organization of iridophores two layers is a novelty that allowed the passage chameleons in record time for an effective camouflage a spectacular parade, while providing thermal protection passive.
The researchers now intend to explore the cellular mechanisms that govern in the iridophores, change nanocrystals mesh, as well as the development of crystalline layers.
Teyssier JA, Saenko SV, van der Marel D, Milinkovitch MC 2015. Photonic crystals cause active colour change in chameleons. Nature Communication 6, http://dx.doi.org/10.1038/ncomms7368