The influence of ultraviolet reflectance differs between conspicuous aposematic signals in neotropical butterflies and poison frogs

Warning signals are often characterized by highly contrasting, distinctive and memorable colors. Both chromatic (hue) and achromatic (brightness) contrast contribute to signal efficacy, making longwave colored signals (red and yellow) that generate both chromatic and achromatic contrast common. Shortwave colors (blue and ultraviolet) do not contribute to luminance perception, yet are also common in warning signals. The presence of UV aposematic signals is paradoxical as UV perception is not universal, and evidence for its utility is at best mixed. We used visual modeling to quantify how UV affects signal contrast in aposematic butterflies and frogs. We found that UV only appreciably affected visual contrast in the butterflies. As the butterflies, but not the frogs, have UV-sensitive vision these results support the notion that UV reflectance is associated with intraspecific communication, but appears to be non-functional in frogs. Consequently, we should be careful when assigning a selection-based benefit from UV reflectance.

警戒信号（aposematic signal）通常以高对比度、独特且令人印象深刻的色彩为特征。色彩（色相）与消色差（亮度）对比度均可提升信号的传递效能，这使得兼具色彩与消色差对比度的长波色彩信号（红色与黄色）成为常见的警戒信号类型。短波色彩（蓝色与紫外线）虽无法对亮度感知产生贡献，但同样常见于警戒信号之中。紫外警戒信号的存在看似矛盾，因为紫外感知并非普遍存在，且其效用的相关证据充其量也是混杂不一的。我们借助视觉建模（visual modeling）量化了紫外线对蝶类与蛙类警戒色信号对比度的影响。研究发现，紫外线仅对蝶类的视觉对比度产生显著影响。由于蝶类（而非蛙类）具备紫外敏感视觉，上述结果支持了“紫外反射与种内通讯相关”这一观点，但在蛙类中似乎并无功能。因此，在将基于选择的益处归因于紫外反射时，我们应当保持谨慎。