Song frequency correlates with latitude and individual body size in the cicada Mogannia formosana Matsumura (Hemiptera: Cicadidae)

Analyses of acoustic variation between and within populations can help to clarify the evolution and diversification of cicada calling songs. In this study, we analyzed the acoustic variation in the calling song of Mogannia formosana within Taiwan and between Taiwan and Green Island to assess the effects of geographic locations. Furthermore, chorusing males in the Green Island population were recorded and collected from the same habitat site during the same time period to investigate the relationship between individual body size and the acoustic features of calling songs. Among populations of M. formosana, we found that most of the acoustic variation in M. formosana calling songs was associated with frequency parameters, in which six frequency parameters changed significantly with latitude on the island of Taiwan. In contrast, temporal parameters, which were associated with principal components corresponding to less acoustic variation than that of the first principal component, were also found to be significant among populations but did not show consistent trends of difference with latitude. However, the geographically isolated Green Island population exhibited the lowest number of short echemes in segment B, which is the diagnostic structure employed to separate M. formosana from other M. species. This finding suggests that the temporal pattern of segment B in the calling songs of M. formosana might be important for both population differentiation and interspecific recognition. In a chorus of the Green Island population, the sound frequency of the last short echeme was found to be significantly correlated with individual body size. The possible role played by sexual selection in shaping sound frequency as a result of its reliable association with body size was discussed. We suggest that, in comparison with temporal elements, the frequency elements of segment B in calling songs of M. formosana in chorus can serve as a more reliable indicator of body size for female mate choice.