A shared gene but distinct dynamics regulate mimicry polymorphisms in closely related butterfly species

Sex-limited polymorphisms, like mating strategies in male birds and mimicry in female butterflies, are widespread across the tree of life and frequently adaptive. Considerable work has been done exploring why genetic variation resulting in sex-limited morphs is generated and maintained, yet little is known about their molecular and developmental genetic basis. In the butterfly genus Papilio (subgenus Menelaides), multiple species have female-limited polymorphism: females develop either mimetic or non-mimetic wing colour patterns, and each polymorphism is controlled by allelic variation at doublesex (dsx). Across several species, we found that alternative female morphs develop male-like colour patterns when we knock down dsx expression, establishing that dsx controls both sexual dimorphism and polymorphism. We also found that mimetic dsx alleles have unique spatiotemporal expression patterns between two species, Papilio lowii and Papilio alphenor. To uncover the downstream genes involved in the polymorphism between species, we compared RNA-seq data from P. lowii with previous work in P. alphenor. While some canonical wing patterning genes are differentially expressed in females of both species, the temporal patterns of differential expression are notably different. Our results indicate that, despite the putative ancestral co-option and shared use of dsx among closely related species, the mimicry switch functions through distinct underlying mechanisms.