Effect of male body size on sperm precedence in the polyandrous butterfly Pieris napi L. (Lepidoptera: Pieridae)

Male Lepidoptera produce an ejaculate during copulation thatcontains both sperm and accessory gland nutrients and may functionas paternal investment and/or male mating effort Several studieshave examined how ejaculates function as paternal investment,but few have determined the influence of sperm competition onmale investment This study examines the effect of male bodysize on sperm precedence in the polyandrous butterfly Pierisnapi L. We used male body mass as an indicator of the size ofejaculate transferred and found that relative male size hada significant effect on paternity. The offspring of twice-matedfemales showed a low incidence of mixed paternity. Larger malesobtained the majority of fertilizations, and the degree of second-malesperm precedence was influenced by relative body size of matingmales. In general, second mates obtained fewer fertilizationsthe larger the size of the first mate. The interval betweenthe first and second mating was influenced by the size of thefirst male mate Females first mated to small males remated soonerthan females first mated to larger males Our results suggestthat large males may have a selective advantage over small maleswhen both a male's fertilization success and a female's refractoryperiod are influenced by the size of ejaculate transferred.Furthermore, the effect of male body size on the proportionof offspring sired lends support to the hypothesis that spermcompetition has played a major role in the evolution of ejaculatesize.