Sexual selection for intermediate optimum in Chorthippus brunneus (Orthoptera: Acrididae)

Individual males of the grasshopper, Chorthippus brunneus, differ significantly in several components of their calling songs which are used to attract and stimulate females. In a ‘round robin’ experiment involving 21 males, the variance in male mating success was greater than expected by chance. Males were ranked and correlations were sought between this rank and characteristics of the males. A significant negative correlation was found between rank and deviation of individual males from the overall mean syllable length, indicating stabilizing selection on this character, which may be involved in species recognition. In individual competitions between males there was a tendency for the more actively singing male to mate with the female.