Study Species and Sample Collection
We captured three to five individuals of each of 27 species of agamid lizards (28 populations, which included genetically differentiated populations of Ctenophorus pictus from Victoria and South Australia, 79 individuals, 186 tissue samples) from various locations in Victoria, South Australia and Western Australia between September 2015 and January 2016 (Figure 1; Table S6). All individuals were adult males for all but one species, Ctenophorus maculosus , for which we sampled a female because it is the only species in our dataset with reverse sexual dichromatism. All lizards were sampled during the spring-summer breeding season to record seasonal coloration in some species of the genus Diporiphora . Study species were selected based on the presence or seasonal expression of yellow-red coloration (as described in literature; Cogger 2018; Melville 2019), and to encompass the range of phylogenetic diversity within Australian agamids from a broad geographic and climatic range. Lizards were humanely euthanised with an intraperitoneal injection of sodium pentabarbitone (150 mg/ kg) after the lizard was calm in cloth bag and within 48 hours of capture. Immediately post-mortem, we took standardized photos from which we extracted RGB values and derived measures of hue, saturation and luminance (full details in Supplementary Information). Although these photos do not capture ultraviolet wavelengths, spectral data show that integument colours of species in this study have very little UV reflectance (Supplementary Information, Figure S4). Additionally, lizard colours derived from RGB have been shown to have a statistically similar distribution to near-simultaneously collected spectral data mapped in avian and agamid lizard visual color space (Smith et al. 2016). We took skin samples for liquid chromatography-mass spectrometry (LC-MS) analysis and stored the samples in methanol at -20°C in foil-wrapped tubes.