Unexpected colour pattern variation in mimetic frogs: implication for the diversification of warning signals in the genus Ranitomeya

Predation is expected to promote uniformity in the warning colouration of defended prey, but also mimicry convergence between aposematic species. Despite selection constraining both colour-pattern and population divergence, many aposematic animals display numerous geographically structured populations with distinct warning signals. Here, we explore the extent of phenotypic variation of sympatric species of Ranitomeya poison frogs and test for theoretical expectations on variation and convergence in mimetic signals. We demonstrate that both warning signal and mimetic convergence are highly variable and are negatively correlated: some localities display high variability and no mimicry while in others the phenotype is fixed and mimicry is perfect. Moreover, variation in warning signals is always present within localities, and in many cases, this variation overlaps between populations, such that variation is continuous. Finally, we show that coloration is consistently the least variable element and is likely of greater importance for predator avoidance compared to patterning. We discuss the implications of our results in the context of warning signal diversification and suggest that, like many other locally adapted traits, a combination of standing genetic variation and founding effect might be sufficient to enable divergence in colour pattern.捕食作用被认为会推动具有防御能力的猎物的警戒色趋于统一，同时也会促进不同警戒色（aposematic）物种间的拟态趋同。尽管选择压力同时约束了体色图案与种群分化，但许多具有警戒色的动物仍演化出众多具有地理结构特征的种群，且各自拥有独特的警戒信号。本研究针对同域分布的箭毒蛙属（Ranitomeya）物种的表型变异程度展开探究，并对拟态信号变异与趋同的理论预期进行验证。研究结果显示，警戒信号与拟态趋同均存在显著变异，且二者呈负相关关系：部分采样点的种群具有高度变异且无拟态现象，而另一些种群的表型则固定不变且拟态完美。此外，各采样点内部始终存在警戒信号的变异，且在多数情况下，不同种群间的变异存在重叠，使得整体变异呈现连续性。最后，研究表明体色始终是变异程度最低的特征，相较于体色图案，其在躲避天敌方面可能发挥着更为关键的作用。本研究结合警戒信号多样化的研究背景探讨了所得结果的生物学意义，并提出：与诸多其他局部适应性性状一样，现存遗传变异与奠基者效应的共同作用，足以促成体色图案的分化。