Linkage disequilibrium and natural selection for mimicry in the Batesian mimic Hypolimnas misippus (L.) (Lepidoptera: Nymphalidae) in the Afrotropics
On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore- and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London.