Abstract
Climatic gradients frequently predict large-scale ecogeographical
patterns in animal coloration, but the underlying causes are often
difficult to disentangle. We examined ecogeographical patterns of
reflectance among 343 European butterfly species and isolated the role
of selection for thermal benefits by comparing visible and near-infrared
(NIR) wavebands. NIR light accounts for ~50% of solar
energy but cannot be seen by animals so functions primarily in thermal
control. We found that reflectance of both dorsal and ventral surfaces
shows thermally adaptive correlations with climate. This adaptive
variation was more prominent in NIR than visible wavebands and for body
regions (thorax-abdomen and basal wings) that are pivotal for
thermoregulation. Thermal environments also predicted the reflectance
difference between dorsal and ventral surfaces, which may be due to
modulation between requirements for heating and cooling. These results
highlight the importance of climatic gradients in shaping the
reflectance properties of butterflies at a continent-wide scale.