Disentangling thermal from alternative drivers of reflectance in jewel beetles: a macroecological study

To predict future colour-climate relationships, it is important to distinguish thermal drivers of reflectance from other evolutionary drivers. This can be achieved by comparing relationships between climate and colouration in ultraviolet-visible (UV-Vis) and near-infrared (NIR) light, separately; yet NIR properties have been measured in very few species. Here, we used jewel beetles (Coleoptera: Buprestidae) as models to identify climatic drivers of reflectance because jewel beetles have highly diverse colouration, a wide distribution, and are often active in hot conditions. Specifically, we tested the association between climate, body size and reflectance using a phylogenetic comparative analysis for three wavebands (UV-Vis, NIR, total). Results showed that reflectance of jewel beetles was more strongly predicted by body size than climate. NIR and total reflectance was not associated with climate, but larger beetles had higher NIR reflectance. For UV-Vis reflectance, small beetles were darker in warmer and more humid environments, whereas there was no association with climate for large beetles. Our study suggests that reflectance variation of jewel beetles is not driven by thermal requirements and highlights the importance of considering NIR reflectance when evaluating explanations of colour effects on thermoregulation.