Mating asymmetry resulting from sexual conflict in the brachypterous grasshopper Podisma sapporensis

摘要

We explored why interpopulation crosses often yield mating asymmetry in the grasshopper Podisma sapporensis. Previous studies show that when local populations are crossed, mating frequency differs significantly between the 2 types of heterotypic mating. Mating asymmetry has been explained by 3 hypotheses: female choice, sexual conflict, or the consequences of bottlenecking events (Kaneshiro's hypothesis). The present study assessed which hypothesis best explained the observed mating patterns. Each test population was crossed with populations used in the previous studies. Of the 10 combinations of interpopulation crossing, 6 exhibited significant asymmetry in the frequency of heterotypic mating, 2 had marginal P values, and 2 exhibited symmetry. The mating frequency of one sex of a test population was mainly determined by the mating propensities of 2 crossed populations, but no interactions were detected between the populations. Conspicuous mating asymmetry arose when the 2 populations had greatly different mating propensities (i.e., the combination of vigorous males in 1 population and receptive females in the other population). In contrast, when 2 populations with similar female receptivity were crossed, the mating tended to be assortative. The results of crossing of ancestral and derived chromosomal races do not support Kaneshiro's hypothesis. Furthermore, the finding that mating propensities for both sexes vary greatly among populations does not agree with the female choice hypothesis. In conclusion, our results are consistent with the sexual conflict hypothesis, which postulates that mating vigor/receptivity varies geographically due to antagonistic coevolution between the sexes.