Pre- and postbreeding costs of parental investment

Costs of reproduction are traditionally defined as reductions in the potent ial for future fitness contributions, induced by current reproductive inves tments, i.e. postbreeding costs. However, preparation for breeding and pare ntal care may expose parents to survival costs already before offspring ind ependence. Such prebreeding survival costs have only rarely been considered in the context of life history evolution. Theoretical analyses show that p re- and postbreeding costs have differential effects on fitness, and a dist inction between these two systems of costs may therefore be of crucial impo rtance in analyses of optimal parental investment. With prebreeding costs, optimal parental investment is lower than with post breeding costs, ceteris paribus. We illustrate this in a simple analysis of optimal clutch size, and provide general conditions for optimal ditch size with prebreeding and postbreeding costs, respectively. Through their diffe rential effects on fitness, systems of costs may also influence and direct the evolution of behavioural and physiological patterns associated with par ental investments. The distinction between pre- and postbreeding costs provides new perspectiv es on costs of reproduction that may prove fruitful in the future developme nt of life history theory. It also allows analyses of optimal life historie s under reproductive costs in semelparous organisms. As predation may be an important mechanism behind prebreeding survival costs, we emphasize the ro le of predation and anti-predatory behaviour in the evolution of life histo ries and breeding behaviour.