Elucidating the mechanistic basis for the trade-off between reproduction and immunity in female D. melanogaster. Robin A. Schwenke, Brian P. Lazzaro. Cornell University, Ithaca, NY.

   Immune defense and reproduction are critical components of fitness and have been documented to trade-off in numerous biological systems. Although these trade-offs are pervasive, the underlying physiological mechanisms remain poorly defined. Female Drosophila melanogaster become more susceptible to infection after mating, suggesting a physiological trade-off between reproduction and immunity. Additionally, prior results have shown that females are genetically variable for the severity of this trade-off suggesting the potential for an evolutionary trade-off. We are interested in unraveling the mechanistic basis for this trade-off in order to understand the function and evolution of the traits involved. Using a series of egg development mutants, we found that the effect of mating on immunity is erased in the absence of a germline, but that the trade-off persists if egg production is halted downstream of germline formation. Furthermore, we have found that mated females remain immunosuppressed even after egg production returns to virgin levels due to sperm depletion. This finding suggests that post-mating immunosuppression is driven by a permanent physiological shift away from virgin homeostasis. We are currently investigating the role endocrine signaling in regulating this shift toward decreased immune defenses in mated females.