Distinct developmental mechanisms influence sexual dimorphisms in the milkweed bug Oncopeltus fasciatus

Sexual dimorphism is common in animals. The most complete model of sex determination comes from Drosophila melanogaster, where the relative dosage of autosomes and X chromosomes leads indirectly to sex-specific transcripts of doublesex (dsx). Female Dsx interacts with a mediator complex protein encoded by intersex (ix) to activate female development. In males, the transcription factor encoded by fruitless (fru) promotes male-specific behaviour. The genetics of sex determination have been examined in a small number of other insects, yet several questions remain about the plesiomorphic state. Is dsx required for female and male development? Is fru conserved in male behaviour or morphology? Are other components such as ix functionally conserved? To address these questions, we report expression and functional tests of dsx, ix and fru in the hemipteran Oncopeltus fasciatus, characterizing three sexual dimorphisms. dsx prevents ix phenotypes in all sexes and dimorphic traits in the milkweed bug. ix and fru are expressed across the body, in females and males. fru and ix also affect the genitalia of both sexes, but have effects limited to different dimorphic structures in different sexes. These results reveal roles for ix and fru distinct from other insects, and demonstrate distinct development mechanisms in different sexually dimorphic structures.

Automated summary

Sexual dimorphism is common in animals, and the fruit fly Drosophila melanogaster provides a complete model of sex determination. The interaction between female doublesex (dsx) and intersex (ix) proteins activates female development, while the male-specific behavior is promoted by the fruitless (fru) transcription factor. The genetics of sex determination have been studied in a few other insects, but some questions about the ancestral state remain unclear. By studying the hemipteran Oncopeltus fasciatus, researchers found that dsx prevents ix phenotypes and dimorphic traits in all sexes. Both ix and fru genes are expressed in females and males, affecting the genitalia and distinct dimorphic structures in different sexes. These findings reveal distinct roles for ix and fru in Oncopeltus fasciatus and demonstrate diverse developmental mechanisms in sexually dimorphic structures.