Acoustic adaptations of periodical cicadas (Hemiptera: Magicicada)

Abstract

We studied the trade-off between traits that function in mate attraction and those that function in enemy avoidance by contrasting features of acoustic communication in cicadas differentially at risk to predators in the same environment. Two genera of North American cicadas were studied: Magicicada and Tibicen. Magicicada species of periodical cicadas, with 17-year life cycles, seek mates in dense aggregations of calling males that are made possible by the relative ineffectiveness of predators to control their numbers. During the breeding season, Magicicada are so abundant that they satiate their predators. From their relative freedom from predation, it is to be expected that traits for attracting mates are emphasized in Magicicada compared with the more solitary genus Tibicen, which reproduce at much lower densities. Males of solitary species are expected to sing more loudly and at low pitch because both features enhance long-distance transmission. These two features were confirmed by measurement. Magicicada septendecim appears to be the most divergent species, evolutionarily, in terms of an unusually sharply tuned sound resonating system, low resonant frequency, and quietness of its song that cannot be entirely explained by body size. These characteristics represent adaptations to the problem of communicating unambiguously to females at close range in a loud and heterogeneous sound environment. Sensitivity to predators, parasitoids, and congeneric species may also have shaped the evolution of their communication systems. © 2007 The Linnean Society of London.