Data for butterfly near-infrared adaptation research

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 animal-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 climatic factors including temperature and precipitation. This
adaptive variation was more prominent in NIR than animal-visible wavebands
and for body regions (thorax-abdomen and basal wings) that are most
important 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.