Males Can Benefit from Sexual Cannibalism Facilitated by Self-Sacrifice

In a number of species, males are cannibalized by females after mating (reviewed in [1, 2]), and some males actually appear to facilitate their own cannibalism (reviewed in [3]). Such self-sacrifice can evolve if being eaten sufficiently enhances either fertilization success (mating effort) or offspring number or fitness (paternal effort). While there is some support for the mating-effort hypothesis, few studies have found support for paternal effort. We used two experiments to test the paternal-effort hypothesis in the dark fishing spider, Dolomedes tenebrosus. Males of this species provide themselves as a material contribution: they spontaneously die during copulation and are subsequently eaten by females. In support of the paternal-effort predictions, when females were allowed to consume their mating partner, we found large and significant increases in (1) the number, (2) the size, and (3) the survivorship of the offspring. Similar benefits were not seen when females were allowed to consume a cricket in lieu of a male, suggesting that it is the consumption of the male's body per se that is responsible for these fitness benefits. Together, our results suggest that D. tenebrosus males can benefit from self-sacrifice behavior through paternal effort. Such behavior may be particularly likely to evolve when high rates of postcopulatory cannibalism trap males into investing in their first mate instead of investing in acquiring additional matings and/or if strong first-male sperm precedence reduces the benefits of both investing in additional matings and paternity protection.