Sexual conflict underlying external female genital mutilation in spiders: assessing whether females benefit from...

External female genital mutilation (EFGM) is a type of traumatic mating in which males damage female genitalia, resulting in the loss of female re-mating ability. This study examined whether sexual conflict underlies EFGM by examining the possible female reproductive costs from the decreased number of matings in spider, Cyclosa argenteoalba. The female typically receives sperm from a male twice during a mating bout. We manipulated both the number of matings and the number of male partners of females and compared their reproductive outputs. The results indicated that females receiving sperm three times-equivalent to one and a half matings from two males-laid more egg sacs with more eggs per egg sac than control females that received sperm twice from one male. The control females laid more egg sacs and fewer eggs per egg sac than females that received sperm once. There was no significant difference in reproductive output between the control females and females that received sperm twice from the two males. These results indicate that females benefit from multiple matings but not from mating with multiple males, supporting the sexual conflict hypothesis. Our study has implications for our understanding of the evolution of harmful mating.