The Cost of Biparental Sex Under Individual Selection

Models of evolutionarily stable strategies are presented, which were designed to determine whether the disadvantage of anisogamous biparental sex is due to the cost of male allocation or to the cost of meiosis. The results show that (1) the cost of biparental sex is due to gene sharing given mutations increasing the proportion of non-cleistogamous parthenogenetic ova in cosexual individuals and (2) the cost of biparental sex is due to male allocation given mutations increasing somatic reproduction in cosexual individuals and mutations increasing partial pathenogenesis in dioecious females. It is suggested that, in general, the cost of biparental sex is due to male allocation when mutations that increase uniparental reproduction affect events before the male-allocation decision, and that the cost of biparental sex is due to gene sharing when mutations that increase uniparental reproduction affect events that come after the male-allocation decision.