Data and original code for: Polarization and reflectance are linked to climate, size and mechanistic constraints in a group of scarab beetles

Beetles exhibit an extraordinary diversity of brilliant and colourful
appearances and optical effects invisible to humans. Their underlying
mechanisms 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 in a
group of optically diverse 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 larger beetles have higher
visible reflectivity in drier environments. Unexpectedly, near-infrared
(NIR) reflectivity was not correlated with ecological variables. However,
we found a correlation between humidity and polarization (chiral
nanostructures). We identified trade-offs between optical properties:
beetles without polarization-associated nanostructures had higher NIR
reflectivity. By contrast, visible reflectivity was 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.