Male‐like females, mimicry and transvestism in butterflies (Lepidoptera: Papilionidae)

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Abstract
When a butterfly species has a polymorphic female, with one of the forms closely resembling the male, it is customary to suppose that this form is ancestral, and that the ‘odd’ forms have arisen later. R. I. Vane‐Wright, on the other hand, has suggested that in some species the male‐like form may be a ‘transvestite’ female, the ancestral form of the female having been strikingly unlike the male. As later‐derived forms are usually, but not always, genetically dominant to ancestral forms, we can make some choice between these hypotheses by discovering the dominance relations of the male‐like and the ‘odd’ forms of the female. In the mimetic Papilio aegeus the male‐like form is shown to be recessive to the ‘odd’ (mimetic) form, as has essentially been the case in all other butterflies so far investigated. Papilio phorcas is now shown to be the exception: the ‘odd’ (non‐mimetic) form is recessive to the male‐like form. We conclude that usually the male‐like form is ancestral, but that P.phorcas may be an authentic example of ‘transvestism’, or the ‘transfer’ of male epigamic colour to the female of the species. The yellow, male‐like pattern of the mimetic Papilio dardanus may be dominant or recessive to the mimetic forms according to the genetic background: largely recessive in Madagascar, and southern and western Africa, dominant to most forms in Ethiopia, and probably dominant to one mimetic form but recessive to the others in Kenya. All female dardanus patterns, both mimetic and yellow, are strongly dominant to both female phorcas patterns in P. dardanus × P. phorcas hybrids (P. ‘nandina’). The simplest explanation of this situation is that the male‐like pattern of dardanus is ancestral, and that dominance has become locally reversed in Ethiopia. The dominance relations, and the sex‐ or autosomal‐linkage of two forms can be determined without pedigree‐breeding, simply by observing a few offspring each from a large number of wild‐caught females.

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