Quantification of sexual selection on male song structure in wild populations of sagebrush crickets, Cyphoderris strepitans (Orthoptera: Haglidae)

While many studies have measured multivariate selection on sexual signals, few have done so in wild populations. Sagebrush crickets are well suited for such investigations because non-virgin males are unambiguously marked with hindwing wounds inflicted by female nuptial feeding. We measured the shape and strength of sexual selection acting on male song by recording the songs of virgin and non-virgin males captured from three wild populations. To determine how male song is influenced by female song preference, we conducted a companion study in which synthesized male songs were broadcast to females in choice trials. Multivariate selection analysis revealed a saddle-shaped fitness surface with the highest peak corresponding to longer train and pulse durations, and longer intertrain intervals. Longer trains and pulses likely enhance mate attraction, but selection for longer intertrain intervals suggests that the energetic costs of singing may necessitate recovery "time outs." Playback trials confirmed female preference for longer train and pulse durations, and additionally revealed significant stabilizing selection on dominant frequency, suggesting that the female auditory system may be tightly tuned to the species-specific call frequency. Overall our results showed a complex pattern of multivariate nonlinear selection characterized primarily by strong stabilizing and disruptive selection on male song characteristics.