Müllerian mimicry is a classic example of adaptation, yet Müller’s original theory does not account for the persistence of diversity in mimicry rings, which has been a thorn in the side of one of the oldest models in evolutionary biology. Here, we aimed to assess how well classical Müllerian mimicry can account for the color polymorphism found in chemically defended Oreina leaf beetles, specifically testing its predictions for predator behavior. We also evaluated whether thermoregulation can explain diversity between Oreina mimicry rings. We found that frequencies of each color morph were positively correlated among species, a critical prediction of Müllerian mimicry. Predators learned to associate color with chemical defenses. Learned avoidance of the green morph of one species protected green morphs of another species. Avoidance of blue morphs was completely generalized to green morphs, but surprisingly, avoidance of green morphs was less generalized to blue morphs. This asymmetrical generalization should favor green morphs: indeed, green morphs persist in blue communities, whereas blue morphs are entirely excluded from green communities. We did not find a correlation between elevation and coloration, rejecting thermoregulation as an explanation for diversity between mimicry rings. Biased predation could explain within-community diversity in warning coloration, providing a solution to a longstanding puzzle. We propose testable hypotheses for why asymmetric generalization occurs, and how predators maintain the predominance of blue morphs in a community despite asymmetric generalization.

One dataset contains frequencies of beetles found in natural communities in the Alps. The other contains data from laboratory experiments conducted using Blue Tits as predators on the beetles. Additionally, we include our R script for analysis.