Project description:The female-limited Batesian mimicry polymorphism in Papilio butterflies is an intriguing system for investigating the mechanism of maintenance of genetic polymorphisms. In Papilio polytes, an autosomal region encompassing the sex-determinant gene doublesex controls female-limited mimicry polymorphism. In the closely related species P. memnon, which also exhibits female-limited Batesian mimicry polymorphism, we identified two allelic sequences of the doublesex gene that corresponded exactly with the mimetic and non-mimetic female phenotypes. Thus, the genetic basis of the mimicry polymorphism in P. memnon is similar to that in P. polytes. However, the mimetic and non-mimetic alleles of the two species were not identical, and the divergence of alleles occurred independently in P. memnon and P. polytes. Different mutation-selection processes may have resulted in the convergent patterns of mimicry polymorphism in these Papilio butterflies.
Project description:Tracking allele frequencies is essential for understanding how polymorphisms of adaptive traits are maintained. In Papilio memnon butterflies, which exhibit a female-limited Batesian mimicry polymorphism (wing-pattern polymorphism), two alleles at the doublesex (dsx) locus correspond to mimetic and non-mimetic forms in females; males carry both dsx alleles but display only the non-mimetic form. This polymorphism is thought to be maintained by a negative frequency-dependent selection. By tracking dsx allele frequencies in both sexes at a Taiwanese site over four years, we found that the mimetic allele persists at intermediate frequencies even when the unpalatable model papilionid butterflies (Pachliopta and Atrophaneura species) were very rare or absent. The rates of male mate choice did not differ between the two female forms; neither did insemination number nor age composition, suggesting equivalent reproductive performance of the two forms over time. Our results characterised the temporal dynamics of the mimetic allele frequency in the field for the first time and give insights into underlying processes involved in the persistence of the female-limited Batesian mimicry polymorphism.