Preferential predation of female butterflies and the evolution of batesian mimicry

BATESIAN mimicry, in which a palatable mimic resembles an unpalatable model, functions to protect insect mimics from birds. In butterflies that show batesian mimicry, female-limited mimicry is common 1–3 . The orthodox theory to explain this is sexual selection against males 4–6 . In these theoretical arguments, no difference in predation pressure between the sexes was assumed, but the existence of female-biased predation would enhance the evolution of sex-limited mimicry. To test for differences in attack rate between the sexes, I examined the rates of beak marks on wings of palatable butterflies of Papilionidae and Pieridae, and unpalatable Danaidae. Here I report that females were attacked more frequently than males, though danaids were generally attacked less. The papilionid and pierid males had low attack rates similar to those of danaid females. Analysis of a mathematical model highlighted these tendencies. Comparing a batesian mimetic species and its 'model' species, non-mimetic females were selectively attacked and the males, mimetic females and 'models' were attacked less. Therefore females benefit greatly when they become mimetic, whereas males will benefit much less should they become mimetic. Thus female-limited mimicry will be favoured even if the costs of mimicry to both sexes are the same.