Distinct developmental mechanisms influence sexual dimorphisms in the milkweed bugOncopeltus fasciatus

Abstract

Sexual dimorphism is common in animals. The most complete model of sex determination comes fromDrosophila melanogaster, where the relative dosage of autosomes and X chromosomes leads indirectly to sex-specific transcripts ofdoublesex(dsx). Female Dsx interacts with a mediator complex protein encoded byintersex(ix) to activate female development. In males, the transcription factor encoded byfruitless(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. Isdsxrequired for female and male development? Isfruconserved in male behaviour or morphology? Are other components such asixfunctionally conserved? To address these questions, we report expression and functional tests ofdsx,ixandfruin the hemipteranOncopeltus fasciatus, characterizing three sexual dimorphisms.dsxpreventsixphenotypes in all sexes and dimorphic traits in the milkweed bug.ixandfruare expressed across the body, in females and males.fruandixalso affect the genitalia of both sexes, but have effects limited to different dimorphic structures in different sexes. These results reveal roles forixandfrudistinct from other insects, and demonstrate distinct development mechanisms in different sexually dimorphic structures.