Environmental changes can greatly affect animal hosts, impacting both physiology and behavior. Changes that alter the fitness of the organism are most important because they determine which traits continue to subsequent generations. Work across species suggests that organisms have evolved mechanisms to detect the immunological strength of a prospective mate. Using Drosophila melanogaster as a model organism, we are investigating the relationship between declines in male fitness and infection with the natural pathogen Providencia rettgeri. If a fly survives acute infection with this bacteria, the fly is chronically infected for the remainder of its life. Little was known, however, about how chronic infection impacts male reproduction. We find that chronically infected male flies produce fewer offspring when mated to groups of virgin females. We examined the mechanism behind this reproductive defect by testing the impact of chronic infection on both mate choice and sperm replenishment.
Mate choice is influenced by the composition of a male’s cuticular hydrocarbons (CHCs), which are long-chain fatty acids found on the external surface of most insects that mediate a variety of host processes including desiccation resistance, communication, and mate choice. We assessed the ability of chronic infection to influence mate choice by both determining how infection changes the CHC profile of the male fly and how infection influences selection of the infected male fly in a competitive mating assay. In addition, we determined the sperm replenishment capability of chronically infected flies by successively mating the fly with virgin females and scoring viable offspring. Throughout all of these assays, male flies were also assessed for either pathogen load or survival to allow correlation of phenotypes with severity of infection. We are currently using genetic mutants in various pathways to determine the pathways responsible for modulating the effects during infection. Ultimately, this research will provide a mechanistic example of how sensory detection of infection status impacts male reproduction.