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

Abstract

Antipredator defenses and warning signals typically evolve in concert. However, the extensive variation across taxa in both these components of predator deterrence and the relationshipãbetween them are poorly understood. Here we test whether there isãa predictive relationship between visual conspicuousness and toxicityãlevels across 10 populations of the color-polymorphic strawberryãpoison frog, Dendrobates pumilio. Using a mouse-based toxicity assay,ãwe find extreme variation in toxicity between frog populations. Thisãvariation is significantly positively correlated with frog colorationãbrightness, a viewer-independent measure of visual conspicuousnessã(i.e., total reflectance flux). We also examine conspicuousness fromãthe view of three potential predator taxa, as well as conspecific frogs,ãusing taxon-specific visual detection models and three natural backgroundãsubstrates.We find very strong positive relationships betweenãfrog toxicity and conspicuousness for bird-specific perceptual models.ãWeaker but still positive correlations are found for crab and D. pumilioãconspecific visual perception, while frog coloration as viewed byãsnakes is not related to toxicity. These results suggest that poisonãfrog colors can be honest signals of prey unpalatability to predatorsãand that birds in particular may exert selection on aposematic signalãdesign. © 2011 by The University of Chicago.