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Data and original code for: Explaining the diversity of optical effects in Christmas beetles: climate, history, and mechanisms

<p><span>Beetles exhibit an extraordinary diversity of brilliant and colourful appearances. The mechanisms producing these optical effects have received some attention, but we know little about the ecological variables driving their evolution. Here we investigated environmental correlates of reflectivity and circular polarization produced by a combination of pigments and structures in optically diverse Christmas beetles (Scarabaeidae: Rutelinae). We quantified the optical properties of 261 specimens representing 46 species using spectrophotometry and calibrated photographs. Then, we examined associations between these properties and environmental variables such as temperature, humidity, and vegetation cover, controlling for body size and phylogenetic relatedness. Our results showed that larger beetles have higher reflectivity and occur in drier environments. Unexpectedly, near-infrared (NIR) reflectivity was not correlated with ecological variables. We observed no universal ecogeographical pattern for polarization but identified trade-offs with other optical properties: beetles without polarization-associated nanostructures had higher NIR reflectivity. Visible reflectivity seems less affected by nanostructures and is instead negatively correlated with the accumulation of pigments such as melanin. Our study highlights the value of a macroecological approach for testing alternative hypotheses to explain the diversity of optical effects in beetles and to understand the link between structure and function.</span></p>