Function and interaction of sex determination genes in the hemimetabolous insect Oncopeltus fasciatus

The regulation and evolution of sex is a fundamental question in developmental biology. Sex determination mechanisms have only been studied in holometabolous insects, or insects with complete metamorphosis. In addition to being closely related to several human and agricultural pests, O. fasciatus is a member of the most closely related clade to these extensively studied holometabolous insects. Determining the genetic basis of sex in an outgroup such as O. fasciatus will shed light on how sex evolves. Candidate genes were chosen from the sex determination pathway of D. melanogaster. Transcript levels of transformer-2A, transformer-2B, intersex, and fruitless were examined at each developmental stage using quantitative PCR; a full list of significant pairwise comparisons is available in Supplementary Tables 1 and 2. Functional analyses of candidate genes virilizer, female-2-d, transformer-2, male-specific lethal-2, male-specific lethal-3, intersex, and fruitless were done using RNA interference methods. Results indicate that these sex determination genes play different roles in O. fasciatus compared to the established D. melanogaster model--most genes do not appear to have a role in sex determination. Additionally, although the genes fruitless and intersex are conserved, the phenotypes produced by the knockdown are non sex-specific. Interaction data suggests that fruitless promotes intersex expression--a novel interaction at the most downstream point of the sex determination pathway. These data support the theory that although upstream sex-determining genes vary widely across insect groups, downstream genes remain conserved.