Poison frog colors are honest signals of toxicity, particularly for bird predators

Antipredator defenses and warning signals typically evolve in concert. However, the extensive variation across taxa in both these components of predator deterrence, and the relationship between them, are poorly understood. Here we test whether there is a predictive relationship between visual conspicuousness and toxicity levels across 10 populations of the color polymorphic strawberry poison frog, Dendrobates pumilio. Using a mouse-based toxicity assay, we find extreme variation in toxicity between frog populations. This variation is significantly positively correlated with frog coloration brightness, a viewer-independent measure of visual conspicuousness (i.e. total reflectance flux). We also examine conspicuousness from the view of three potential predator taxa, as well as conspecific frogs, using taxon-specific visual detection models and three natural background substrates. We find very strong positive relationships between frog toxicity and conspicuousness for bird-specific perceptual models. Weaker but still positive correlations are found for crab and D. pumilio conspecific visual perception, while frog coloration as viewed by snakes is not related to toxicity. These results suggest that poison frog colors can be honest signals of prey unpalatability to predators, and that birds in particular may exert selection on aposematic signal design.

反捕食防御与警戒信号通常协同演化。然而，学界对于捕食者威慑作用的这两个组成部分（反捕食防御与警戒信号）在不同类群间的广泛差异，以及二者之间的关联，仍知之甚少。本研究针对体色多态的草莓箭毒蛙（Dendrobates pumilio）的10个种群，检验视觉显眼度与毒性水平之间是否存在预测性关系。本研究采用小鼠毒性实验法，发现不同蛙种群间的毒性存在极端差异。该毒性差异与蛙类体色亮度呈显著正相关；体色亮度是一种不依赖观测者的视觉显眼度量化指标（即总反射通量）。此外，本研究借助类群特异性视觉检测模型与三种天然背景基质，分别从三类潜在捕食者类群以及同种蛙类的视角评估了蛙类的视觉显眼度。针对鸟类特异性感知模型的分析显示，蛙类毒性与视觉显眼度之间存在极强的正相关关系；而在蟹类与草莓箭毒蛙同种个体的视觉感知下，二者虽呈较弱但仍显著的正相关；至于蛇类视角下的蛙类体色，则与毒性并无关联。本研究结果表明，箭毒蛙的体色可作为猎物对捕食者而言不可口的诚实信号，且鸟类可能是驱动警戒信号演化的主要选择压力来源。