Aposematic patterns shift continuously through the life of poison frogs

Color and pattern are often dynamic traits that change throughout an individual's lifetime. Still, long-term shifts in coloration have received limited attention. Dendrobatid poison frogs are a classical system in the study of color and pattern evolution in which both sexual selection and predation avoidance are thought to drive the evolution of color and pattern at the population and species level. Here, we highlight an overlooked axis of pattern diversity, within individual variation, using three species in the genus Dendrobates. We collected longitudinal photographs of individuals at the National Aquarium to test the hypothesis that pattern shifts predictably throughout the lifetimes of individual frogs. In all three species, we found a consistent reduction in the relative area of aposematic color as individuals aged and that the rate of pattern shift did not differ between the sexes. Consequently, within individual variation in coloration may confound inferences from ecological studies that inherently assume individual pattern is static. Finally, we note that using simple and noninvasive photography protocols, animals in zoos and aquaria have the potential to deepen our understanding of how color and pattern change throughout the lifetimes of a wide range of species.

体色与图案往往是伴随个体生命周期动态变化的性状，但长期以来，学界对体色的长期演变的关注却相对不足。箭毒蛙科毒蛙（Dendrobatid poison frogs）是研究体色与图案演化的经典研究类群，学界普遍认为性选择与反捕食压力共同推动了其种群及物种水平上的体色与图案演化。本研究以箭毒蛙属（Dendrobates）的3个物种为研究对象，聚焦此前被忽视的图案多样性维度——个体内变异。我们于国家水族馆（National Aquarium）采集了个体的纵向影像资料，以验证“蛙类个体生命周期内的图案变化具有可预测性”这一假说。研究结果显示，在3个物种中，随着个体衰老，其警戒色（aposematic color）的相对占比均呈持续下降趋势，且图案变化速率不存在性别差异。由此可见，体色的个体内变异可能会干扰那些默认个体图案保持静态的生态学研究的推论。最后，本研究指出，借助简便无创的影像采集方案，动物园及水族馆中的饲养动物有望帮助我们深化对多类物种生命周期内体色与图案变化规律的认知。