The genetics of the mimetic butterfly Papilio polytes L

Abstract

Papilio polytes L. is a mimetic Swallowtail butterfly widely distributed in South East Asia. It has four female forms, three mimetic, and one non-mimetic resembling the monomorphic male in appearance. The various female forms are now shown to be controlled by allelomorphs at a single autosomal locus and not by independent genes as previously thought. The effects of the allelomorphs controlling the mimetic patterns are sex-limited to the female. There is some evidence that the locus is a complex one consisting of two or more tightly linked genes. As in previous investigations into mimicry in Swallowtails the dominance tends to be complete between sympatric forms. The accuracy of the mimicry depends not only on the presence of the appropriate major genes but also on the rest of the gene complex. Thus within a race there is an integrated genetic system and on outcrossing this becomes disturbed, leading to poorer mimicry. The system of modifiers controlling the accuracy of the mimetic pattern is closely paralleled by that in P. dardanus . In particular, in P. polytes f. theseus appears to differ from f. polytes only as a result of the presence of a modifier system, as does f. hippocoon from f. hippocoonides in P. dardanus . In P. dardanus from Ethiopia it was found that specific modifiers adjusting the tail length of mimetic females have been selected for, thus improving the mimicry. An analogous situation has been found in P. polytes although here the control is more effective in that the resulting difference in tail length between the mimetic and non-mimetic forms can be as much as 10 mm, whereas in P. dardanus it rarely exceeds 3 mm. The great similarity in the genetic structure of P. polytes and P. dardanus (as well as P. memnon ) strongly suggests that selection for a mimetic polymorphism results in the evolution of very similar genetic control mechanisms in different species - that is to say it is the nature of the selection rather than the species involved which determines the genetic architecture.