Coarse dark patterning functionally constrains adaptive shifts from aposematism to crypsis in strawberry poison frogs

Ecological specialization often requires tight co-evolution of several traits, which may constrain future evolutionary pathways and make species more prone to extinction. Aposematism and crypsis represent two specialized adaptations to avoid predation. We tested whether the combined effects of color and pattern on prey conspicuousness functionally constrain or facilitate shifts between these two adaptations. We combined data from 17 natural populations of Strawberry poison frogs, Oophaga pumilio with an experimental approach using digitalized images of frogs and chickens as predators. We show that bright coloration often co-occurs with coarse patterning among the natural populations. Dull green frogs with coarse patterning are rare in nature but in the experiment they were as easily detected as bright red frogs suggesting that this trait combination represent a transient evolutionary state towards aposematism. Hence, a gain of either bright color or coarse patterning leads to conspicuou...