The cost of reproduction in callosobruchus maculatus.

The bruchid beetle Callosobruchus maculatus does not feed as an adult. The resources such as energy or nutrients available to it are therefore fixed at emergence. Allocation of resources to processes contributing to one trait must therefore reduce those available for allocation to others and trade-offs between these traits are expected. The present study investigates the trade-off between current and future reproduction, the cost of reproduction, in both females and males of this species taking an explicitly phenotypic approach. The trade-off between adult longevity and lifetime fecundity in females is demonstrated using experimental manipulations of fecundity. It is shown that reduced adult longevity reflects reduced future reproduction and that this trade-off is therefore the cost of reproduction. The inadequacy of phenotypic correlations in demonstrating this trade-off is shown. The allocations of dry weight, water, lipid and energy by females to reproductive and non-reproductive processes are measured. For each resource, the predicted slope of the trade-off between adult longevity and lifetime fecundity is calculated based on that resource being limiting. From a comparison between these predicted slopes and the slope measured using experimental manipulation, it is concluded that none of these resources can be rejected as the limiting resource and that they all may contribute to the trade-off. Males make a non-trivial investment in ejaculate. This investment reduces a male's future reproductive success. To some extent these costs are short-term; the male soon regains his fertility. However, there are also long-term costs due to reduced longevity. The fitness consequences of remating to females are investigated. Fecundity is increased following remating but it is impossible to distinguish between the nutritional and manipulative roles of the ejaculate. Finally, the costs of reproduction are summarised and their generality and implications discussed.