Enigmatic ornamentation eases male reliance on courtship performance for mating success

Female preferences are frequently invoked to explain the widespread occurrence of elaborate male ornaments, yet empirical data demonstrating such preferences are sometimes equivocal or even contradictory. In the wolf spider Schizocosa stridulans, despite evidence of strong female choice, prior research has been unable to link the conspicuous sexually dimorphic foreleg ornamentation of males to their mating success. We conducted three experiments aimed at determining the function of this previously enigmatic ornamentation. Our first two experiments used males with phenotypically modified foreleg phenotypes in simple and complex mating environments in order to examine the relationship between the presence/absence of ornamentation and male mating success. In both experiments, we found no relationship: courtship rate was the sole predictor of mating success. In a third experiment, we used males with naturally varying foreleg ornamentation in mating trials. Ornamentation was subsequently quantified and we again examined the factors influencing male mating success. As in our first two experiments, we found courtship rate to be a good predictor of mating success. Additionally, we discovered that foreleg ornamentation and courtship rate interact to influence male mating success. At low courtship rates, males with more foreleg ornamentation have a mating advantage, whereas at high courtship rates, males with less foreleg ornamentation have a mating advantage. We discuss several potential explanations for these results. In summary, we provide the first evidence of a benefit of foreleg ornamentation in male S. stridulans and suggest that this benefit is realized by the interaction between ornamentation and courtship rate.