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

Aim: To predict future colour- climate relationships, it is important to distinguish thermal drivers of reflectance from other evolutionary drivers. We aimed to achieve this by comparing relationships between climate and coloration in ultraviolet- visible (UV- Vis) and near-infrared (NIR) light, separately. Location: Samples were distributed primarily across Australia and North America, with some from Africa and Asia. Major taxa studied: Coleoptera: Buprestidae. Methods: We used jewel beetles as models to identify climatic drivers of reflectance, because jewel beetles have highly diverse coloration and 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 and total). Results: Reflectance of jewel beetles was more strongly predicted by body size than by climate. NIR reflectance and total reflectance were 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. Main conclusions: Our study suggests that variation in reflectance of jewel beetles is not driven by thermal requirements and highlights the importance of considering NIR reflectance when evaluating explanations of the effects of colour on thermoregulation.

Automated summary

To predict future colour-climate relationships, it is important to differentiate thermal drivers of reflectance from other evolutionary drivers. This study compares the relationships between climate and coloration in UV-Vis and NIR light separately.