Genetic manipulation of insulin/insulin-like growth factor signaling pathway activity has sex-biased effects on Drosophila body size

Abstract

In Drosophila, female body size is approximately 30% larger than male body size due to an increased rate of larval growth. While the mechanisms that control this sex difference in body size remain incompletely understood, recent studies suggest that the insulin/insulin-like growth factor signaling pathway (IIS) plays a role in the sex-specific regulation of growth during development. In larvae, IIS activity differs between the sexes, and there is evidence of sex-specific regulation of IIS ligands. Yet, we lack knowledge of how changes to IIS activity impact growth in each sex, as the majority of studies on IIS and body size use single- or mixed-sex groups of larvae and/or adult flies. The goal of our current study was to clarify the requirement for IIS activity in each sex during the larval growth period. To achieve this goal we used established genetic approaches to enhance, or inhibit, IIS activity, and quantified body size in male and female larvae. Overall, genotypes that inhibited IIS activity caused a female-biased decrease in body size, whereas genotypes that augmented IIS activity caused a male-specific increase in body size. This data extends our current understanding of larval growth by showing that most changes to IIS pathway activity have sex-biased effects on body size, and highlights the importance of analyzing data by sex in larval growth studies.