Data from: Cryptic differences in colour among Müllerian mimics: how can the visual capacities of predators and prey shape the evolution of wing colours?

Antagonistic interactions between predators and prey often lead to co-evolution. In the case of toxic prey, aposematic colours act as warning signals for predators and play a protective role. Evolutionary convergence in colour patterns among toxic prey evolves due to positive density-dependent selection and the benefits of mutual resemblance in spreading the mortality cost of educating predators over a larger prey assemblage. Comimetic species evolve highly similar colour patterns, but such convergence may interfere with intraspecific signalling and recognition in the prey community, especially for species involved in polymorphic mimicry. Using spectrophotometry measures, we investigated the variation in wing coloration among comimetic butterflies from distantly related lineages. We focused on seven morphs of the polymorphic species Heliconius numata and the seven corresponding comimetic species from the genus Melinaea. Significant differences in the yellow, orange and black patches of the wing were detected between genera. Perceptions of these cryptic differences by bird and butterfly observers were then estimated using models of animal vision based on physiological data. Our results showed that the most strikingly perceived differences were obtained for the contrast of yellow against a black background. The capacity to discriminate between comimetic genera based on this colour contrast was also evaluated to be higher for butterflies than for birds, suggesting that this variation in colour, likely undetectable to birds, might be used by butterflies for distinguishing mating partners without losing the benefits of mimicry. The evolution of wing colour in mimetic butterflies might thus be shaped by the opposite selective pressures exerted by predation and species recognition.捕食者与猎物间的拮抗相互作用往往会引发协同进化。对于有毒猎物而言，警戒色（aposematic colours）可作为向捕食者传递的警示信号，发挥保护作用。有毒猎物的色斑模式之所以会发生演化趋同，是因为正密度依赖选择（positive density-dependent selection），以及通过将使捕食者形成避食认知的死亡成本分摊至更大的猎物集群中所带来的相似互利益处。共拟态物种（comimetic species）会演化出高度相似的色斑模式，但这类趋同可能会干扰猎物群落内的种内信号传递与识别，尤其对于参与多态拟态（polymorphic mimicry）的物种而言。本研究采用分光光度法（spectrophotometry），对来自远缘演化支系的共拟态蝴蝶的翅色变异展开了调查，研究对象包括多态物种红带袖蝶（Heliconius numata）的7个色型，以及美脉蛱蝶属（Melinaea）对应的7个共拟态物种。研究检测到两属间翅部黄色、橙色与黑色斑块存在显著差异。随后，基于生理数据构建的动物视觉模型，评估了鸟类与蝴蝶观察者对这类隐蔽差异的感知情况。结果显示，黄色与黑色背景间的对比度所引发的感知差异最为显著。基于该色对比度区分共拟态属的能力，在蝴蝶中评估得到的结果高于鸟类，这表明这类大概率无法被鸟类察觉的色变异，或许可被蝴蝶用于区分交配伴侣，同时不会丧失拟态带来的益处。因此，拟态蝴蝶的翅色演化或许受到捕食压力与物种识别压力这两种相反选择压力的共同塑造。