Data from: Stabilizing selection on individual pattern elements of aposematic signals

Warning signal variation is ubiquitous but paradoxical: low variability should aid recognition and learning by predators. However, spatial variability in the direction and strength of selection for individual elements of the warning signal may allow phenotypic variation for some components, but not others. Variation in selection may occur if predators only learn particular colour pattern components rather than the entire signal. Here, we used a nudibranch mollusc, Goniobranchus splendidus, which exhibits a conspicuous red spot/white body/yellow rim colour pattern, to test this hypothesis. We first demonstrated that secondary metabolites stored within the nudibranch were unpalatable to a marine organism. Using pattern analysis, we demonstrated that the yellow rim remained invariable within and between populations; however, red spots varied significantly in both colour and pattern. In behavioural experiments, a potential fish predator, Rhinecanthus aculeatus, used the presence of the yellow rims to recognize and avoid warning signals. Yellow rims remained stable in the presence of high genetic divergence among populations. We therefore suggest that how predators learn warning signals may cause stabilizing selection on individual colour pattern elements, and will thus have important implications on the evolution of warning signals.警戒信号的变异普遍存在却又充满悖论：理论上较低的变异度应当有助于捕食者对其进行识别与学习。然而，警戒信号各组成单元所承受的选择压力在方向与强度上存在空间异质性，这可能使得部分信号组分出现表型变异，而另一部分则不会。若捕食者仅能学习特定的色彩图案组分而非完整的警戒信号，则选择压力的异质性便可能产生。本研究以具有醒目红斑/白身/黄缘色彩图案的华丽背鳃海牛（Goniobranchus splendidus）为实验对象，对该假说进行验证。我们首先证实，该海牛体内储存的次生代谢产物对海洋生物具有拒食性。通过图案分析，我们发现黄缘在种群内部及种群间均保持稳定；而红斑则在色彩与图案两方面均存在显著变异。在行为学实验中，潜在的鱼类捕食者尖吻扳机鱼（Rhinecanthus aculeatus）会通过黄缘的存在识别并避开警戒信号。即便种群间存在高度的遗传分化，黄缘仍保持稳定。因此我们提出，捕食者对警戒信号的学习方式可能会对各色彩图案组分产生稳定化选择，这对警戒信号的演化具有重要意义。