Mimetic females do not bear reproductive costs: Challenging the sexual selection hypothesis in female-limited mimetic polymorphism in butterflies.

Batesian mimicry has been regarded as classic evidence of adaptation by natural selection, in which a palatable species avoids predation by resembling unpalatable species. In some butterfly species, Batesian mimicry is female-limited and mimetic females coexist with male-like (nonmimetic) females. Why do nonmimetic females continue to exist despite the possible differential predation pressure? One possible hypothesis is a trade-off between the anti-predatory defence and mating success. Specifically, mimetic females may be less attractive to conspecific males as they look like heterospecific butterflies. However, empirical studies based on behavioural data have shown mixed results. Here, we directly investigated female mating frequency by counting spermatophores and compared it between mimetic and nonmimetic females in a Batesian mimetic butterfly, Papilio polytes. The mating frequencies of the two types of females were almost identical in all four studied populations. More than 99% of females copulated at least once regardless of morph. In addition, the spermatophore counts increased with age and did not differ between morphs. Our results strongly suggest that the anti-predatory traits are unlikely to be costly to the reproductive success of mimetic P. polytes females, providing no support for the sexual selection hypothesis regarding maintenance of mimetic polymorphism.