Within-Species Mate Preferences Do Not Contribute to the Maintenance of Sexually Monomorphic Mating Signals in Green Lacewings

Abstract

We know much less about the evolutionary forces and constraints that maintain similar mating displays in females and males than we do about sexually dimorphic mating displays. Both female and male green lacewings have sexually monomorphic vibrational mating signals and are equally choosy against heterospecific mating signals. This similarity in between-species sex roles may explain a large part of the presence of species-specific female signals in these species, but does not necessarily predict why female and male signals are similar. We tested for within-species sex-specific similarities in mate preferences in Chrysoperla lucasina that may contribute to the maintenance of sexually monomorphic mating signals in this species. We found weak preferences and low levels of discrimination for signals with varying fine-scale temporal features (volley duration, period, and volley-duty cycle). The longer signals that both sexes produced in response to playback were sexually monomorphic, but some females and most males also produced shorter signals with significantly reduced volley durations and periods. Notably, all of these signals had indistinguishable volley-duty cycles, the ratio of volley duration to volley period. We propose that mating signals in C. lucasina are maintained in both sexes because of similar between-species mate preferences, but the sexually monomorphic mating signals cannot be attributed to significant within-species mate preferences. What differences are present in within-species sex roles may be resolved by a male-biased signal polymorphism, in long and short signals that are hypothesized to have distinct functions during mate calling and courtship.