doublesex Controls Both Hindwing and Abdominal Mimicry Traits in the Female-Limited Batesian Mimicry of Papilio memnon

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

Sex-limited polymorphisms, such as mating strategies in male birds and mimicry in female butterflies, are widespread across the tree of life and are frequently adaptive. Considerable work has been done exploring the ecological pressures and evolutionary forces that generate and maintain genetic variation resulting in alternative sex-limited morphs, yet little is known about their molecular and developmental genetic basis. A powerful system to investigate this is Papilio butterflies: within the subgenus Menelaides, multiple closely related species have female-limited mimicry polymorphism, with females developing either derived mimetic or ancestral non-mimetic wing color patterns. While mimetic color patterns are different between species, each polymorphism is controlled by allelic variation of doublesex (dsx). Across several species, we found that the mimetic and non-mimetic females develop male-like color patterns when we knockdown 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 color pattern switch between both species, we used RNA-seq in P. lowii and compared the results to 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.

Functional unit of supergene in female-limited Batesian mimicry of Papilio polytes

Supergenes are sets of genes and genetic elements that are inherited like a single gene and control complex adaptive traits, but their functional roles and units are poorly understood. In Papilio polytes, female-limited Batesian mimicry is thought to be regulated by a ∼130 kb inversion region (highly diversified region: HDR) containing 3 genes, UXT, U3X, and doublesex (dsx) which switches non-mimetic and mimetic types. To determine the functional unit, we here performed electroporation-mediated RNAi analyses (and further Crispr/Cas9 for UXT) of genes within and flanking the HDR in pupal hindwings. We first clarified that non-mimetic dsx-h had a function to form the non-mimetic trait in female and only dsx-H isoform 3 had an important function in the formation of mimetic traits. Next, we found that UXT was involved in making mimetic-type pale-yellow spots and adjacent gene sir2 in making red spots in hindwings, both of which refine more elaborate mimicry. Furthermore, downstream gene networks of dsx, U3X, and UXT screened by RNA sequencing showed that U3X upregulated dsx-H expression and repressed UXT expression. These findings demonstrate that a set of multiple genes, not only inside but also flanking HDR, can function as supergene members, which extends the definition of supergene unit than we considered before. Also, our results indicate that dsx functions as the switching gene and some other genes such as UXT and sir2 within the supergene unit work as the modifier gene.