Males under attack: sexual cannibalism and its consequences for male morphology and behaviour in an orb-weaving spider

During their quest to maximize fertilization success, males may be under sexual selection through male–male competition, female choice and/or sexual conflict over mating frequency. In many orb-weaving spiders, mating interactions are characterized by sexual cannibalism, which has been hypothesized to drive the evolution of male morphology and mating behaviour in this group. Here, we investigate sexual selection on male body size, leg length and copulation duration due to sexual cannibalism in the highly sexually dimorphic orb-weaving spider Argiope aurantia. In a controlled laboratory experiment, we analysed male–female interactions for 99 pairs, with the aid of detailed video recordings. We measured selection on males during five selection episodes during the courtship and mating sequences. We found significant selection during the insertion of the first pedipalp, where 23% of males were killed. Larger males with longer legs for their size were more likely to be attacked, but male morphology had no effect on the likelihood of survival. Instead, males that stayed inserted longer (median insertion duration = 3.5 s) were more likely to be killed by the female. However, we did not detect any trade-off between fertilization success and survival during the first insertion. Males that achieved two insertions increased their fertilization success by about 25% compared with males that inserted only once. Our results suggest that sexual cannibalism is not an important contributor to the maintenance of the sexual dimorphism in size or shape (relative leg length) in this species. However, sexual cannibalism does select for very short copulation duration and rapid sperm transfer.