PROJECT SUMMARY There is a fundamental gap in the understanding of how biological sex impacts highly integrated innate immune and metabolic responses to affect individual infection susceptibility. The overall goal of this proposal is to define the role of sex-specific traits in influencing energetic trade-offs that underlie innate immune responses and dictate infection susceptibility. Ancient stressors such as nutritional shortage and pathogenic challenges pushed organisms to develop tightly regulated and highly integrated adaptive metabolic and innate immune responses (referred to as immuno-metabolic responses). Recent studies have shown that the modulation of energy storage and consumption via immuno-metabolic networks is shaped by external environmental pressures as well as internal cues throughout an individual’s life. Specifically, events such as prior infections or developmental growth rates often dictate the allocation of lipid energy storage, resulting in energetic trade-offs that prioritize key fitness traits and contribute to inter-individual variation in susceptibility to infection. Additionally, there are sex-based variations in pathogen susceptibility across taxa. While it is evident that the dysregulation of normal reciprocal interactions between reproductive and immune systems can lead to diseases affecting one or both systems, it is less understood how sex-specific traits involved in reproduction shape metabolic activity, energetic trade-offs, and responses to pathogenic infection. These nebulous connections prompted interest to untangle the complex integration of sex-specific traits, metabolism, and innate immunity through a tractable model. This proposal will use the Drosophila melanogaster genetic model to test the hypothesis that post-mating changes specifically in the female reproductive tissue, but not male, can influence immuno-metabolic responses and energetic trade- offs (lipid storage and usage) that ultimately impact infection susceptibility. Aim I of this proposal will assess the impact of male and female post-mating reproductive changes on immuno-metabolic responses and infection susceptibility. Aim II will leverage recent advances in sequencing techniques to generate a single-nucleus transcriptomic map to describe infection- and sex-dependent gene expression changes, highlighting the integration of biological sex, immunity, and metabolism and the impact of continuous gene interaction on bacterial infection outcome. To be succinct, this proposal intends to show that reproductive physiology specifically in females determines energetic trade-offs that shape immuno-metabolic responses and lead to pathogen susceptibility. Defining the energetic trade-offs that underlie interactions between reproductive activity and immune responses will provide fundamental insight on not just that sexes differ, but how and why they differ when faced by similar pathogens - which may also provide insight into sex-specific pathogen-related d...