![]() ![]() The spatial arrangement of all these cell types generates a broad range of colors and color patterns.ĭespite such a high potential for complexity and diversity, lizards and snakes remain relatively under-represented in evolutionary developmental studies in general, and in analyses of color-pattern evolution in particular (for example, in comparison with other vertebrates or insects). Squamates additionally possess iridophores, which do not contain any pigment but generate structural coloration through interference of light waves with transparent guanine nanocrystals. These pigments are typically either pteridines, which are synthesized in situ from guanosine triphosphate, or carotenoids, which are metabolized from food in the liver and transported to skin via the circulatory system. In addition to melanophores, which produce black/brown melanins, squamates develop xanthophores and erythrophores, containing yellow and red pigments, respectively. In particular, non-mammalian vertebrates, for example, squamates (lizards and snakes), exhibit a broad range of pigmentary and structural colors, generated by different types of chromatophores. Moreover, colors and color patterns are amenable to objective quantification and modeling, providing an opportunity for integrated analyses of phenotypic variation. Indeed, color traits play crucial roles in thermoregulation, photoprotection, camouflage, and visual communication, and can vary extensively among and within species and populations. Vertebrate skin coloration provides a promising model system for exploring the link between genotypes and phenotypes in an ecological and phylogenetic framework. This study opens up new perspectives on Phelsuma lizards as models in evolutionary developmental biology. Our results indicate the need to identify the developmental mechanisms responsible for the control of the size, shape, and orientation of nanocrystals, and the superposition of specific chromatophore types. Precisely colocalized interacting pigmentary and structural elements generate extensive variation in lizard color patterns. Finally, we show that melanophores form dark lateral patterns but do not significantly contribute to variation in blue/green or red coloration, and that changes in the pH or redox state of pigments provide yet another source of color variation in squamates. We validated these results through numerical simulations combining pigmentary components with a multilayer interferential optical model. Most importantly, these interactions require precise colocalization of yellow and red chromatophores with different types of iridophores, characterized by ordered and disordered nanocrystals, respectively. More specifically, we show that 1) the hue of the vivid dorsolateral skin is modulated both by variation in geometry of structural, highly ordered narrowband reflectors, and by the presence of yellow pigments, and 2) that the reflectivity of the white belly and of dorsolateral pigmentary red marks, is increased by underlying structural disorganized broadband reflectors. ResultsĬombining histology, optics, mass spectrometry, and UV and Raman spectroscopy, we found that the extensive variation in color patterns within and among Phelsuma species is generated by complex interactions between, on the one hand, chromatophores containing yellow/red pteridine pigments and, on the other hand, iridophores producing structural color by constructive interference of light with guanine nanocrystals. Here, we used an integrated approach to investigate the morphological basis and physical mechanisms generating variation in color traits in tropical day geckos of the genus Phelsuma. However, the extensive variation in non-melanic pigments and structural colors in squamate reptiles has been largely disregarded. Color traits in animals play crucial roles in thermoregulation, photoprotection, camouflage, and visual communication, and are amenable to objective quantification and modeling. ![]()
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