Density-dependent plasticity of sequential mate choice in a bushcricket (Orthoptera : Tettigoniidae)

Abstract

Mate choice is a common phenomenon in animals and several factors have been proposed as being involved in the acceptance or rejection of a partner. I investigated the effect of population density on the mate-sampling behaviour of female Xederra charactus (bushcrickets). In my study, female bushcrickets adjusted the tactic of sequential mate sampling in response to mate density, visiting a series of up to five different males per night. Under low-density conditions, females visited fewer males in a night and were less likely to reject a copulation attempt than females under high-density conditions. Rejection of a male occurred during 29% of copulations in areas of high population density, but during only 8% in areas of low population density. Moreover, at low densities, females were less likely to reject mates later in the night, which can be interpreted as a reaction to the time constraints of a finite nightly mating period. Females in high-density populations also more often chose males with a higher mass of the spermatophore-producing accessory glands. Due to such choice, females might receive a larger nuptial gift at mating. These results are consistent with tactical models of search behaviour in which females adjust their behaviour to the number of potential mates and the length of the mating period.