Comparative evidence for a cost to males of manipulating females in bushcrickets

Recent theoretical and empirical research on sexual conflict has tended to focus on the costs to females of being manipulated by males. The costs to males associated with the production of manipulative traits have received relatively little attention. In numerous insects, including bushcrickets (Orthoptera: Tettigoniidae), males are known to transfer substances in the ejaculate that inhibit the receptivity of females to further matings in a dose-dependent manner. The aim of this study was to test the prediction that, across bushcricket taxa, larger ejaculates and nuptial gifts will be associated with, on the one hand, longer sexual refractory periods in females and, on the other hand, longer sexual refractory periods in males. Data on the duration of the sexual refractory period in both males and females, together with ejaculate mass, spermatophylax mass, and male body mass, were obtained for 23 species of bushcricket. Both comparative analysis by independent contrasts and species regression revealed a positive relationship, across taxa, between the duration of the female's sexual refractory period and both relative ejaculate mass and relative nuptial gift mass. Positive relationships were also found between the duration of the male's sexual refractory period and both relative ejaculate mass and relative nuptial gift mass, indicating that there is a trade-off between resources spent on spermatophore size and the male's potential mating rate. This appears to be the first comparative evidence that there is a cost to males associated with manipulating the remating behavior of their mates.