Combining Physics and Biology techniques, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores. In addition, we show that a deeper population of iridophores with larger crystals protect them from excessive exposure to solar radiations by reflecting a large proportion of the sunlight power, especially in the near-infrared range.
Chameleons form a highly derived monophyletic group of iguanian lizards that originated in post-Gondwanan Africa around 90 million years ago. Many chameleons, and panther chameleons (Furcifer pardalis) in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Combining microscopy, photometric videography and photonic band-gap modelling, we show that:
- chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores, and
- that a deeper population of iridophores with larger crystals reflects a substantial proportion of the sunlight power, especially in the near-infrared range.
The organisation of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons that allows some species to combine efficient camouflage with spectacular display, while providing passive thermal protection.
Additional info is available on the ‘Chameleon Colour Change’ page and in the original article (ref. below).
This multidisciplinary project has been performed as close collaboration between the LANE and the lab of Dirk van der Marel (Quantum Materials Group, UniGE).
The chameleon project is embedded into two research consortia:
- The ‘United-Living-Colors.ch’ consortium (funded by the Swiss National Foundation SINERGIA program) investigating the complex interactions between light and the vertebrate skin and how they generate a variety of phenomena of significant fundamental and applied interest;
- The ‘EpiPhysX’ consortium (funded by SystemsX.ch), with the aim to understand how epithelial tissues achieve their complexity.
Much additional information is available in the original article:
Photonic Crystals Cause Active Colour Change in Chameleons
Teyssier J., Saenko S.V., van der Marel D., M.C. Milinkovitch
Nature Communications 6, 6368 (2015)