Biased predation could promote convergence yet maintain diversity within Müllerian mimicry rings of Oreina leaf beetles

Abstract

Müllerian mimicry is a classic example of adaptation, yet Müller’s original theory does not account for the diversity often observed in mimicry rings. Here, we aimed to assess how well classical Müllerian mimicry can account for the color polymorphism found in chemically defended Oreina leaf beetles by using field data and laboratory assays of predator behavior. We also evaluated the hypothesis that 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.