Iridescence and thermal properties of Urosaurus ornatus lizard skin described by a model of coupled photonic structures

Abstract

Abstract This research shows that the morphological characteristics of the external microstructure of the beautiful skin of the Urosaurus ornatus lizard contribute to the explanation of the origin of their iridescent and thermal properties. High-resolution scanning electron microscopy studies revealed that the skin surface of the U. ornatus lizard is constituted by a semi-ordered array of hexagonal photonic crystals with sub-micrometric structural parameters. The iridescence properties of the ventral patch and dorsal surface of the U. ornatus lizard were numerically simulated modeling both surfaces by a set of coupled photonic crystals with structural parameters proposed from statistical measurements of the lattice parameter and holes diameter of its skin surface. The dorsal surface showed the ability to reflect visible light and at least in a significant range the ultraviolet and near infrared radiation. A complete photonic band gap for the transverse magnetic polarization mode of the incident light in both dorsal and ventral surfaces was predicted by calculations. The spectral reflectance and the structure of photonic bands obtained explain the reflection of the infrared radiation by the dorsal surface which might help to the thermoregulation of the lizard body. The results obtained suggest that the selective reflection of incident light performed by the photonic structural array defined on the skin surface of the U. ornatus has a significant contribution to its apparent color.