NUTRITION MEDIATES REPRODUCTIVE TRADE-OFFS WITH AGE-SPECIFIC MORTALITY IN THE BEETLE CALLOSOBRUCHUS-MACULATUS

Trade-offs between mortality and reproduction play a central role in t heories of life history and of senescence. Yet the fundamental questio n of how reproduction affects mortality is unresolved. We simultaneous ly manipulated both egg production and adult food availability in the beetle Callosobruchus maculatus and measured their effects on age-spec ific mortality. We show that there are two distinct mortality trade-of fs of egg production. An early trade-off is observed at ages <18 d and is conditional on current adult nutrition; it is potentially related to energy exhaustion. The late trade-off is observed after 20 d of age , is progressive, and occurs despite the availability of current adult diet; it is potentially related to senescence. The expression of both mortality trade-offs depends on the interaction of early reproduction and nutritional state at the time of reproduction. Food availability at the time of high egg production completely mitigates the early mort ality trade-off and lowers the late mortality trade-off by approximate to 12%. Most mechanistic explanations for the tradeoff between egg pr oduction and survival have assumed that eggs compete for the allocatio n of nutrients that are necessary for survival. However, experiments t ypically alter only egg production or nutrition, and cannot distinguis h between nutrient allocation and alternative mechanisms where some di rect, permanent somatic insult results from reproduction. By manipulat ing both egg production and nutrient availability, we distinguish betw een these alternatives and unambiguously demonstrate that nutrient all ocation can be a mechanism for mortality trade-offs.