Data from: Ultraviolet and yellow reflectance but not fluorescence is important for visual discrimination of conspecifics by Heliconius erato

Toxic Heliconius butterflies have yellow hindwing bars that – unlike their closest relatives – reflect ultraviolet (UV) and long wavelength light, and also fluoresce. The pigment in the yellow scales is 3-hydroxy-DL-kynurenine (3-OHK), found also in the hair and scales of a variety of animals. In other butterflies like pierids with color schemes characterized by independent sources of variation in UV and human-visible yellow/orange, behavioral experiments have generally implicated the UV component as most relevant to mate choice. This has not been addressed in Heliconius butterflies, where variation exists in analogous color components, but moreover where fluorescence due to 3-OHK could also contribute to yellow wing coloration. In addition, the potential cost due to predator visibility is largely unknown for the analogous well-studied pierid butterfly species. In field studies with butterfly paper models we show that both UV and 3-OHK yellow act as signals for H. erato but attack rates by birds do not differ significantly between the models. Furthermore, measurement of the quantum yield and reflectance spectra of 3-OHK indicates that fluorescence does not contribute to the visual signal under broad-spectrum illumination. Our results suggest that the use of 3-OHK pigmentation instead of ancestral yellow was driven by sexual selection rather than predation.

有毒袖蝶属（Heliconius）蝴蝶的后翅带有黄色条带——与它们的近缘类群不同，该条带可反射紫外线（UV）与长波长光，同时还会发出荧光。其黄色鳞片中的色素为3-羟基-DL-犬尿氨酸（3-hydroxy-DL-kynurenine, 3-OHK），该色素广泛存在于多种动物的毛发与鳞片中。在粉蝶科（Pieridae）等蝴蝶类群中，其配色的紫外光与人类可见的黄/橙色组分存在独立的变异来源，相关行为实验普遍认为紫外光组分在配偶选择中发挥核心作用。但这一结论尚未在袖蝶属蝴蝶中得到验证：该类群存在类似的颜色组分变异，且由3-OHK介导的荧光同样可能对其黄色翅色形成产生贡献。此外，针对这类被充分研究的粉蝶类群，其因被捕食者识别而带来的潜在代价仍在很大程度上尚不明确。我们借助蝴蝶纸制模型开展的野外实验表明，紫外光与3-OHK介导的黄色均能作为H. erato的视觉信号，但不同模型组间的鸟类攻击率并无显著差异。此外，对3-OHK的量子产率与反射光谱的测量结果显示，在广谱光照条件下，荧光并未对视觉信号产生贡献。本研究结果表明，袖蝶属蝴蝶选择以3-OHK色素沉着替代祖先型黄色翅色，是由性选择而非捕食压力驱动的。