Hunger-dependent female receptivity leads to variable optimal polyandry with equal fitness in a nuptial gift-giving spider

Female mating decisions are often plastic, dependent on the environment. In the nuptial gift-giving spider Pisaura mirabilis, the optimal number of matings for females, i.e., the number that maximizes fitness, depends on prey availability and is regulated by hunger-dependent receptivity. We determined the lower and upper optimal number of matings for females (at high and low prey availability, respectively) and test the hypothesis that females that obtain the optimal number of matings will achieve that same reproductive success independently of what the optimal number is. In laboratory experiments, females were offered 0, 1, 2, or 3 house flies per day as supplementary feeding and were presented daily with 4 gift-carrying males until oviposition. Fecundity, oviposition latency, egg hatching success, and the number of live spiderlings were independent of the level of supplementary feeding. For females, mating and aggression toward males (gift-stealing and sexual cannibalism) are alternative ways of compensating for low foraging success. We confirmed 2-3 as the minimum optimal number of matings. The maximum optimal number of matings varied between 12 and 22-24 depending on the females' level of aggression. Female behavioral plasticity allows them to decouple their fitness from dependence on environmental prey availability through hunger-dependent receptivity.