The role of predators in maintaining the geographic organization of aposematic signals

Selective predation of aposematic signals is expected to promote phenotypic uniformity. But while uniform within a population, numerous species display impressive variations in warning signals among adjacent populations. Predators from different localities learning to avoid distinct signals while performing intense selection on others are thus expected to maintain such a geographic organization. We tested this assumption by placing clay frog models, representing distinct color morphs of the Peruvian poison-dart frog Ranitomeya imitator and a non conspicuous frog, reciprocally between adjacent localities. In each locality, avian predators were able to discriminate between warning signals; the adjacent exotic morph suffered up to four times more attacks than the local one and two times more than the non conspicuous phenotype. Moreover, predation attempts on the exotic morph quickly decreased to almost nil, suggesting rapid learning. This experiment offers direct evidence for the existence...