Pre- and Postbreeding Costs of Parental Investment

Abstract

Costs of reproduction are traditionally defined as reductions in the potential for future fitness contributions, induced by current reproductive investments, i.e. postbreeding costs. However, preparation for breeding and parental care may expose parents to survival costs already before offspring independence. Such prebreeding survival costs have only rarely been considered in the context of life history evolution. Theoretical analyses show that preand postbreeding costs have differential effects on fitness, and a distinction between these two systems of costs may therefore be of crucial importance in analyses of optimal parental investment. With prebreeding costs, optimal parental investment is lower than with postbreeding costs, ceteris paribus. We illustrate this in a simple analysis of optimal clutch size, and provide general conditions for optimal clutch size with prebreeding and postbreeding costs, respectively. Through their differential effects on fitness, systems of costs may also influence and direct the evolution of behavioural and physiological patterns associated with parental investments. The distinction between preand postbreeding costs provides new perspectives on costs of reproduction that may prove fruitful in the future development of life history theory. It also allows analyses of optimal life histories under reproductive costs in semelparous organisms. As predation may be an important mechanism behind prebreeding survival costs, we emphasize the role of predation and anti-predatory behaviour in the evolution of life histories and breeding behaviour.