Association between external female genital mutilation and securing paternity in a spider

Males sometimes injure their partner physically or physiologically during mating. While harmful mating is assumed to incur fitness costs, it is thought to confer increased paternity for males; this advantage may have driven the evolution of harmful mating. To date, two spider species are known to exhibit external female genital mutilation (EFGM), in which males remove a scape, a small projection on female's external genitalia, to secure their paternity. This study investigated whether a similar phenomenon occurs in Cyclosa ginnaga to assess whether EFGM is commonly associated with paternity securing in spiders. Two consecutive staged mating using a unmated female and two males was conducted and female genitalia was inspected after mating. Results showed that while EFGM occurred among C. ginnaga, the mutilation rate was less than half that of the two previously studied species. Mated females, irrespective of whether they experienced mutilation, attacked the second males that courted them. Consequently, most mating trials ended without successful copulation due to the retreat of the second male, and EFGM was seldom responsible for the failure of the second mating. These results do not support the hypothesis that EFGM evolved because it secured paternity for mutilator males.