Fighting costs stabilize aggressive behavior in intersexual conflicts

We analyze the evolution of aggressive behavior in intersexual conflicts, w ith a special reference to mate guarding behavior in crustaceans. An analys is of a discrete-strategy game shows that an ESS with only one of the sexes being aggressive prevail if fighting costs or fitness values of winning ar e asymmetric. Non-aggressiveness of both sexes is stable if fighting behavi or is very costly for females and if the cost is at least partly paid indep endent of the strategy of the opponent. Most interestingly, the solutions o f both sexes being aggressive prevails only if both sexes have some probabi lity of winning, and if fighting costs are small. Second, we solve for the expected levels of aggressiveness in a game with continuous strategies. The form of the fighting cost function largely determines the stability of the solution. When fighting cost increases linearly with aggressiveness, mutua l aggressiveness fluctuates cyclically instead of stabilizing at an ESS. Ho wever, if there is an asymmetry in fitness payoffs, a solution with only th e sex having most to lose being aggressive alone is possible. With quadrati cally increasing fighting costs an ES combination of mutual aggressiveness may exist. It is predicted that fights between the sexes should be hardest when payoffs are symmetric, and that an overt behavioral conflict will alwa ys take place as long as there is a fitness loss to each of the sexes if lo sing the conflict and both sexes have a chance to win. We discuss the model s in the context of fights preceding precopulatory guarding, but the models offer a general frame for analyzing any intersexual conflict.