Males mate with multiple females to increase offspring numbers in a nursery web spider

Males are often expected to benefit from mating with multiple females; however, in species where females are highly cannibalistic, achieving multiple matings may be a difficult task. When males employ strategies to avoid sexual cannibalism, it is presumed that there are benefits associated with survival-e.g. increased fitness associated with more mating opportunities. In the nursery web spider (Pisaurina mira), all males attempt to avoid sexual cannibalism by wrapping female's legs in silk prior to copulation. If males are unsuccessful, however, there are fitness benefits obtained by both sexes that are associated with their consumption-heavier and longer-lived offspring. Regardless, we hypothesize that P. mira males can achieve higher fitness by avoiding sexual cannibalism. Specifically, we predict that males can and will mate with multiple females and that mating with multiple partners benefits males. To test these predictions, we conducted 1) laboratory assays to determine if males will mate with multiple females and 2) field assays to determine natural sex ratios, density, and female and male movement patterns. Finally, 3) we used our field data to construct a mathematical model that predicts natural male encounter rates with potential mates. We found that male P. mira will mate with multiple females and that increased mating numbers leads to increased offspring production. Our model suggests that under natural conditions, males have the opportunity to mate with multiple females. Overall, our findings strongly suggest that P. mira males are likely to benefit from avoiding sexual cannibalism through increased mating opportunities.