Female mate choice in the lek-mating system of periodical cicadas Magicicada cassini and M. decim: Selection for male body size, dominant courtship song frequency and pathogen avoidance

Broods of periodical cicadas (Homoptera, Cicadidae; Magicicada spp.) spend either 13 or 17 years underground before emerging en masse and mating within about a 4-week period. Changes in mean size of adult male periodical cicadas were monitored and found to increase over the adult life stage, resulting from earlier death of smaller males. In nature, mean size of successfully mated males was greater than the mean of unmated males until late in the season when no smaller males were left. Based on data collected from natural populations, experiments involving female choice of males, and female responses to courtship recordings, I conclude that females choose their mates based on male courtship song frequency. Because I found a strong relationship between dominant frequency of courtship song and volume of male abdomen, these data suggests females listen to male courtship song as a way of assessing abdomen volume and thereby overall body size. I conclude by suggesting advantages females gain from using song frequency to assess potential mates: Song is an honest indicator of size for healthy males, and most likely a good predictor of pathogen infection as stage-1 Massospora cicadina fill the empty abdominal resonating chamber in infected males. This contagious stage of the fungal pathogen only occurs in the first 15 days of the emergence, during which all females (in nature and in experiments) avoided small-sounding males. I suggest females effectively avoid infected males by assessing male courtship song to detect stage-1 infection during the critical early season, resulting in less female stage-2 fungal infections late season. Female choice for large males may be a consequence of female choice for healthy males by means of choosing mates with lower frequency songs.