The Benefits of Tying Up Your Mate
Males and females share the same goal in sexual reproduction (increased fitness), yet specialized morphologies and/or behaviors can evolve in one or both of the sexes that serve to increase one sex's reproductive fitness, sometimes at a cost to the other. In the nursery web spider, Pisaurina mira, males restrain females prior to copulation by wrapping them with silk (silk wrapping). We test the hypothesis that silk wrapping evolved to benefit males. Specifically, we test tow predictions: (1) silk wrapping increases the number of insertions (i.e. opportunities to transfer sperm) that a male can obtain and (2) silk wrapping reduces a male's likelihood of being sexually cannialized. To test these, we randomly assigned males to a (i) wrap (control) or (ii) no wrap treatment prior to pairing them with a female. We prevented males from silk wrapping by covering their spinnerets with dental silicone. For control males, we placed dental silicone on the male's abdomen. In support of our hypothesized benefit to males, we found that silk wrapping (1) increases the number of insertions a male can obtain and (2) reduces rates of sexual cannibalism. While this finding demonstrates a mating benefit of silk wrapping for males, the putative fitness consequences, to both males and females, remain unknown.