The costs of mating and egg production in Callosobruchus seed beetles

Abstract

The net cost of reproduction and the trade-off between reproduction and life span are affected by many male and female adaptations. Because several of these adaptations are sexually selected, we expect the cost of reproduction to be affected by sexual selection. For example, traits favoured in males by sexual selection may increase costs of mating for females. We conducted a series of experiments where we independently varied female exposure to males and access to oviposition substrates in six congeneric seed beetle species (Callosobruchus spp.). These experiments allowed us to partition the cost of reproduction for females into the cost of mating and the cost of egg production. The costs and benefits of a single mating in terms of effects on female life span varied markedly between species. In some species, females lived for longer after mating once but others had a shortened life span. Lifelong cohabitation with males resulted in a shortened life span for females of all species, but the extent to which cohabitation reduced female life span varied between species. We also found partial support for a depressed lifetime egg production as a result of cohabitation with males. Collectively, our results show that the costs and benefits of mating vary markedly within this clade of closely related and ecologically uniform species. We conclude that key traits, which influence the economics of sexual interactions and reproduction, have evolved rapidly in this model system.