Female nursery web spiders ( Pisaurina mira ) benefit from consuming their mate

The often coincidental involvement of cooperation and conflict in animal reproduction is epitomized by sexual cannibalism, which can lead to obvious male costs while simultaneously providing direct benefits to developing offspring. Male nursery web spiders ( Pisaurina mira ) avoid postcopulatory sexual cannibalism by wrapping females with silk. Here, we test the hypothesis that this silk wrapping results in a loss of consumption cost for females. In specific, we hypothesize that females lose out on potential fitness benefits associated with cannibalizing their mating partners. To test this, we paired females with males that were experimentally manipulated to prevent the silk wrapping of females, thereby increasing the likelihood of sexual cannibalism. Females either did not kill their mate, and thus consumed nothing, or did kill their mate. If females killed their mating partner, we allowed them to consume the male, consume nothing, or consume a cricket. We found no effect of female or male body sizes on the likelihood of females killing their mate. While our treatments did not affect the number of offspring females produced, females that consumed either a male or a cricket produced egg sacs faster than females that consumed nothing, suggesting a benefit of increased postcopulatory food consumption. Further, only females that ate a male had heavier and longer lived offspring, suggesting a benefit of sexual cannibalism specifically. Our results support the hypothesis that females can receive fitness benefits associated with sexual cannibalism.