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 theories of life history and of senescence. Yet the fundamental question of how reproduction affects mortality is unresolved. We simultaneously manipulated both egg production and adult food availability in the beetle Callosobruchus maculatus and measured their effects on age-specific mortality. We show that there are two distinct mortality trade-offs 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 mortality trade-off and lowers the late mortality trade-off by approximate to 12%. Most mechanistic explanations for the tradeoff between egg production and survival have assumed that eggs compete for the allocation of nutrients that are necessary for survival. However, experiments typically alter only egg production or nutrition, and cannot distinguish between nutrient allocation and alternative mechanisms where some direct, permanent somatic insult results from reproduction. By manipulating both egg production and nutrient availability, we distinguish between these alternatives and unambiguously demonstrate that nutrient allocation can be a mechanism for mortality trade-offs.