Chemical Ecology of Poisonous Butterflies: Model or Mimic? A Paradox of Sexual Dimorphisms in Müllerian Mimicry

Abstract

A number of butterfly species are toxic or unpalatable against predators by developing mechanisms either to biosynthesize such noxious elements de novo or to acquire directly from the poisonous host plants for their own defense. Most of these “poisonous butterflies” exhibit aposematically colored wing patterns that are often associated either with Batesian or Mullerian mimicry species to form a “mimicry ring.” This review focuses on unpalatable chemical elements potentially operating in three typical mimicry rings: (1) the tiger Danaus mimicry ring, (2) the Idea mimicry ring, and (3) the red-bodied swallowtail mimicry ring, in association with their mimetic wing patterns. Female-limited polymorphisms are a common feature of the Batesian mimicry but not in Mullerian mimicry, because such diversification is unfavorable for the models. I present here some unique cases of sexual dimorphisms within the putative Mullerian mimicry complexes. A Danaus chrysippus-mimicking nymphalid, Argyreus hyperbius, is a typical example of the female-limited dimorphic mimics. However, A. hyperbius were found to be poisonous with toxic cyanogenic glycosides (linamarin and lotaustralin). Likewise, a pipevine swallowtail, Atrophaneura alcinous, which sequesters toxic aristolochic acids, exhibits sexually dimorphic color patterns (male, black; female, smoky brown). A sympatric diurnal zygaenid moth, Histia flabellicornis, is mimetic to A. alcinous males rather than the females and stores cyanogenic glycosides. The moth is regarded as a Mullerian ally that may have stabilized the wing coloration mutually with those of A. alcinous males. On the contrary, a diurnal “swallowtail moth,” Epicopeia hainesii, mimics the brighter wing color of A. alcinous females. Possible adaptation mechanisms on these paradoxical mimicry patterns are discussed.