Sexual behavior in North American cicadas of the genera Magicicada and Okanagana.

Abstract

If potential mates have heritable quality variations, and if the benefits of choosing a superior mate are greater than the costs, selection favors mate choice. Mate choice leads to the evolution of complex, sexually-selected behaviors and morphologies for both mate advertisement and mate evaluation. The seven species of 13- and 17-year periodical cicadas (<italic>Magicicada </italic> spp.) have complex courtship and mating behaviors, suggesting a long history of sexual selection. Males join mixed-species singing aggregations attractive to sexually receptive females, who answer male calls with wing flick signals. Females could exercise precopulatory choice (1) during early stages of courtship when males call and females answer, or (2) during late stages of courtship when male and female approach and make physical contact; or females could exercise postcopulatory choice by remating with a higher quality male. Alternatively, females could benefit more from selecting appropriate times or places for mating than from choosing among potential partners. This study demonstrates that female <italic>Magicicada</italic> signal only in response to males of their own species; thus species-level mate discrimination occurs in the early stages of sexual rapprochement. Such discrimination against heterospecifics is evident in the pattern of reproductive character displacement between <italic>M. tredecim</italic> and <italic>M. neotredecim</italic>, a newly described species: Male signals and female response criteria have evolved increased distinctiveness where these two species co-occur. There is little evidence of active female discrimination among conspecific males: Although variations in phenotypic symmetry affect male likelihood of mating, such variations in male mating success are due to indirect mate choice, not evolved choice mechanisms. Postcopulatory mate choice also appears unlikely; although the seminal plug resulting from matings is not a barrier to future copulations, and although females sometimes remate, female remating is better explained by the need to replenish sperm stores than by the exercise of an evolved postcopulatory choice mechanism. Contrasts between the mating system of <italic>Magicicada</italic> and another cicada genus, <italic>Okanagana </italic>, suggest hypotheses for how the <italic>Magicicada</italic> mating system may have evolved. Understanding the <italic>Magicicada</italic> mating system has general relevance to improving theoretical understanding of mate choice, reproductive character displacement, life cycle evolution, and sexual selection.