Many chameleons, and panther chameleons 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. Here, 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.
Combining histology, electron microscopy and photometric
videography techniques with numerical band-gap modelling, here
we show that chameleons have evolved two superimposed
populations of iridophores with different morphologies and
functions: the upper multilayer is responsible for rapid structural
colour change through active tuning of guanine nanocrystal
spacing in a triangular lattice, whereas the deeper population of
cells broadly reflects light, especially in the near-infrared range.
This combination of two functionally different layers of
iridophores constitutes an evolutionary novelty that allows some
species of chameleons to combine efficient camouflage and
dramatic display, while potentially moderating the thermal
consequences of intense solar radiations.
