Geographic variation in the calling song of the field cricket Gryllus bimaculatus (Orthoptera: Gryllidae) and its relevance to mate recognition and mate choice

For Gryllus bimaculatus (Orthoptera: Gryllidae), a comparison was made of the prediction from species recognition theory that stabilizing selection acts on mate recognition traits and that of sexual selection that predicts diversifying selection on mate recognition traits. The calling songs and morphometrics of four populations of field crickets from South Africa were compared. Song characteristics generally showed less between-population variation than did morphometric variation. This applied in particular to the song characteristics known to be important in species recognition. Within-population variation of species recognition traits were significantly smaller than for other call traits as well as morphometric traits. This is consistent with the expectation that stabilizing selection occurs for species recognition traits within populations as well as throughout their geographical ranges. No song traits correlated significantly with body size. Our study suggests that the calling song traits involved in mate recognition lack the variation required for sexual selection to operate. However, the amount of variation inherent in some of the other song parameters of field crickets still has the potential to give rise to sexual selection based on traits other than body size.