Supplementary Material from Climate is a strong predictor of near-infrared reflectance but a poor predictor of colour in butterflies

Colour variation across climatic gradients is a common ecogeographical pattern;yet there is long-standing contention over underlying causes, particularly selec-tion for thermal benefits. We tested the evolutionary association betweenclimate gradients and reflectance of near-infrared (NIR) wavelengths, whichinfluenceheatgainbutarenotvisibletoanimals.Wemeasuredultraviolet(UVA), visible (Vis) and NIR reflectance from calibrated images of 372 butterflyspecimens from 60 populations (49 species, five families) spanning the Austra-lian continent. Consistent with selection for thermal benefits, the associationbetween climate and reflectance was stronger for NIR than UVA–Vis wave-lengths. Furthermore, climate predicted reflectance of the thorax and basalwing, which are critical to thermoregulation; but it did not predict reflectanceof the entire wing, which has a variable role in thermoregulation dependingon basking behaviour. These results provide evidence that selection for thermalbenefits has shaped the reflectance properties of butterflies.