Symmetry in the songs of crickets

Acoustic signals produced by males are often subject to sexual selection. The mechanism of song production in crickets is well documented. Cricket songs are said to be characterised by almost pure tones of constant frequency. However, contrary to previous work, we show that cricket songs exhibit frequency modulation to varying degrees, dependent on the degree of asymmetry in the sound resonators or harps. Recent studies of sexually selected traits suggest that size and symmetry may reflect male quality. The harps of crickets exhibit directional asymmetry to a degree that is directly related to the degree of fluctuating asymmetry in a measure of body size. We show that females prefer pure tones of low carrier frequency, characteristic of large symmetrical harps. Directional asymmetry may thus convey reliable information regarding male quality encoded in the male's song.