Evolutionary consequences of a trade-off between parental effort and mating effort.

I investigate the joint evolution of male and female strategies in a dioecious population where individuals can increase their access to mates by attacking or threatening rivals. In some species where individuals can increase their mating success in this way, both sexes allocate resources to parental effort. There may be a trade-off between parental effort and mating effort (for conflict over access to mates). If so, what factors must be included in the model for parental effort by both sexes to be evolutionarily stable? I analyse a simple game theoretic model that allows conflict over access to mates. Three versions of this model are analysed. In the simplest version, variation among individuals of each sex is allowed only in their total parental effort. The more elaborate versions of the model also allow variation in the parental investment per offspring. When this type of variation is allowed, a pair of male and female strategies can only be evolutionary stable if one sex alone contributes all parental effort. However, when non-heritable variation in the resources available to individuals is introduced (the third version of the model), parental effort by both sexes can be maintained.