Sexual conflict, which is expected to be ubiquitous among polygamous species, is known to occasionally result in male adaptations that are harmful to females. One theoretical model indicates that males may benefit from physically harming their mates by triggering a “terminal investment” reproductive response by them. Using dynamic programming, we explore how females optimize their lifetime egg allocation, how selection acts on males to exploit such allocation, and how females respond to resist this exploitation. The model reveals alternative female response pathways; one of the most effective of which is simply to forgo plasticity in egg allocation. By switching to a fixed reproductive schedule, females reduce their vulnerability to male manipulations. The results predict that terminal investment should be rare. In addition, terminal investment should occur at higher frequency among monogamous species, where male harm is never adaptive, than among polygamous species. Another unique conclusion of our model is that male harm should be exclusively or preferentially directed at older females and/or females in poor condition.
