Female secondary sexual traits in spiders: Adaptive interpretations of the sternum projection in the pholcid Holocnemus pluchei

Successive matings affect copulatory courtship but not sperm transfer in a spider model

Previous studies have reported that males augment their reproductive success by increasing the number of females with which they copulate, and that such copulations are not energetically demanding in terms of trivial sperm production costs. However, we now know that males do pay reproductive costs. As males mate successively, a reduction in the performance of copulatory behaviours would be expected, as well as in the number of sperm transferred. Here we compared the duration of courtship, mating and post-insemination phase, the number of genital and non-genital copulatory courtship occurrences, and the number of sperm transferred in successive matings in Holocnemus pluchei spider males. As matings increased in males, there was no effect on the duration of courtship, mating or post-insemination phase. Interestingly, genital copulatory courtship varied in successive copulations depending on male size, but there was no change in the number of sperm transferred. In addition, the occurrence of non-genital copulatory courtship decreased along successive copulations. The negative effects of successive matings on copulatory courtship indicate that these behaviours are costly for males, except for the number of sperm transferred. Our research lays the foundation for future studies on male costs as a function of mating history in spiders.

Copulatory behaviour increases sperm viability in female spiders

One remarkable reproductive feature in animals with internal fertilization is a reduction in sperm viability over time in females. Whether this reduction is driven by male–male competition and/or cryptic female choice is unclear. From the perspective of cryptic female choice, we postulated that sperm viability is affected by a particular male copulatory behaviour. In this study, we investigated the following aspects: (1) sperm viability in mated females vs. males; (2) whether sperm viability varies temporally after mating; and (3) whether male copulatory behaviour covaries positively with sperm viability within females. We used the spider Holocnemus pluchei, whose males use several copulatory behaviours to court females. We found that females that stored sperm for 4 or 15 days showed no difference in sperm viability but had lower sperm viability compared with males, and males that performed a longer post-insemination behaviour had higher sperm viability inside the female. It is unclear how sperm viability is reduced and how male post-insemination behaviour affects this. It is possible that extending copulation allows males to induce females to keep sperm alive for longer. This result is predicted by theory whereby males induce females to facilitate sperm to reach and fertilize eggs based on male postcopulatory behaviour.