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

Recent theoretical and empirical research on sexual conflicthas tended to focus on the costs to females of being manipulatedby males. The costs to males associated with the productionof manipulative traits have received relatively little attention.In numerous insects, including bushcrickets (Orthoptera: Tettigoniidae),males are known to transfer substances in the ejaculate thatinhibit the receptivity of females to further matings in a dose-dependentmanner. The aim of this study was to test the prediction that,across bushcricket taxa, larger ejaculates and nuptial giftswill be associated with, on the one hand, longer sexual refractoryperiods in females and, on the other hand, longer sexual refractoryperiods in males. Data on the duration of the sexual refractoryperiod in both males and females, together with ejaculate mass,spermatophylax mass, and male body mass, were obtained for 23species of bushcricket. Both comparative analysis by independentcontrasts and species regression revealed a positive relationship,across taxa, between the duration of the female's sexual refractoryperiod and both relative ejaculate mass and relative nuptialgift mass. Positive relationships were also found between theduration of the male's sexual refractory period and both relativeejaculate mass and relative nuptial gift mass, indicating thatthere is a trade-off between resources spent on spermatophoresize and the male's potential mating rate. This appears to bethe first comparative evidence that there is a cost to malesassociated with manipulating the remating behavior of theirmates.