Effect of Male Mating History and Body Size on Ejaculate Size and Quality in Two Polyandrous Butterflies, Pieris napi and Pieris rapae (Lepidoptera: Pieridae)

Abstract

1. The ability of males to remate repeatedly has a dramatic effect on their lifetime reproductive success. Moreover, nutrients transferred to females during copulation increase a male's investment in reproduction. In this study we examined the effect of male mating history and body size on ejaculate size and quality in two polyandrous butterflies, Pieris napi and Pieris rapae. 2. The interval between first and second matings had a strong effect on the size and protein content of ejaculates. Males mated twice in one day produced second ejaculates corresponding to a third of the size of the first ejaculate, whereas males remated two days later transferred a second ejaculate just as large as that produced in their first mating. Males remating one day after their first mating transferred second ejaculates of intermediate size. In a similar pattern, the absolute amount of protein contained in ejaculates increased as the number of days between matings increased. 3. The relative protein content did not differ between first and second ejaculates when males were remated one, two or three days after their first mating. However, second ejaculates transferred by males mating twice in the same day contained a significantly higher percentage of protein. 4. Male ejaculates are costly to produce as shown by the fact that copulation durations were longer and ejaculates smaller in matings involving recently mated males. 5. Male body size influenced ejaculate size but not protein content of first ejaculates. However, smaller males produced larger ejaculates, relative to their body size, than large males. 6. Males do not refrain from mating until they can produce a full-sized ejaculate. This suggests that males maximize their fitness by mating as often as possible, even in a mating system where male investment in ejaculates has a substantial effect on the number and quality of offspring sired.