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