INTERSEXUAL CONFLICT OVER PRECOPULA DURATION IN MATE GUARDING CRUSTACEA

Precopulatory guarding in Crustacea is usually analyzed as a male deci sion problem. We suggest an alternative possibility that precopula is established as a result of intersexual conflict over precopula duratio n. Such a conflict can be expected when the male optimum for precopula duration exceeds the female optimum. As a result, males should start precopulatory attempts earlier, while females should resist until clos e to receptivity. Our analysis reveals two potential sources of confli ct: (1) sexual differences in survival probabilities before and during the mate-guarding; and (2) sexual differences in the probability of f inding a mate. The latter is perhaps a more probable source of interse xual conflict, since male biased operational sex ratios are common in mate-guarding Crustacea. The former requires that female moulting cycl e is synchronous, whereas the latter may operate in populations with a synchronous moulting cycles as well. We further studied the expected i ntensity of behavioural conflicts in terms of expected present and fut ure fitness gains. In the beginning of the female moulting cycle, ther e is no conflict. Conflict arises as males start the guarding attempts and females are motivated to resist, and ceases with a decrease in th e female's motivation to resist. Several assumptions and predictions o f the model are discussed and compared with the behavioural patterns o bserved in the aquatic isopod Idotea baltica.