2008 Thanatosis as an adaptive male mating strategy in the nuptial gift-giving spider Pisaura mirabilis

Males and females often experience different optima in mating rate, which may cause evolution of female resistance to matings and male counter adaptations to increase mating rate. Males of the spider Pisaura mirabilis display a spectacular mating behavior involving a nuptial gift and thanatosis (death feigning). Thanatosis in a sexual context is exceptional and was suggested to function as an antipredation strategy toward potentially cannibalistic females. If thanatosis serves as a protection strategy, males should death feign in response to female aggression or when they are more vulnerable to attack. We tested these predictions in a factorial design: males that were handicapped (1 leg removed) and hence vulnerable and control males were paired with females that were more or less aggressive intrinsically (measured toward prey). In mating trials, we recorded the tendency of males to death feign, copulation success, and copulation duration. In addition, we investigated the effect of female mating status (virgin or mated) on these male mating components. Intrinsically aggressive females showed increased mating aggression toward males. Neither female aggressiveness, mating status, nor male vulnerability increased the propensity of males to perform thanatosis. Instead, death-feigning males were more successful in obtaining copulations and gained longer copulations. Hence, our results suggest that thanatosis functions as an adaptive male mating strategy to overcome female resistance. All males were capable of performing thanatosis although some males use it more frequently than others, suggesting a cost of death feigning which maintains the variation in thanatosis during courtship. Key words: coevolution, death feigning, male mating effort, nuptial gift, polyandry, sexual cannibalism. [Behav Ecol