Monandry and polyandry as alternative lifestyles in a butterfly

Butterflies show considerable variability in female mating frequency, ranging from monandrous species to females mating several times in their lifetime. Degree of polyandry also varies within species, with some females only mating once and others mating multiply. Previous studies have shown that one reason for female multiple mating is to obtain nutritious male donations that both increase the longevity of females and result in higher lifetime fecundity. Despite the presence of male nutrient donations, some females of the green-veined white butterfly (Pieridae: Pieris napi) never mate more than once. In this study, we examined this apparent paradox. We assessed to what degree polyandry is under genetic control by a full-sib analysis, and we also estimated the broad sense heritability of female lifetime fecundity in singly mated females. Both polyandry and lifetime fecundity have a genetic component. However, degree of polyandry appears to be traded off against reduced longevity when denied the opportunity to mate more than once. It is possible that female P. napi display different reproductive strategies, with some females relying on male donations to realize their potential fecundity and others relying on their own resources for egg production. In nature, polyandrous females may be prevented from mating multiply due to unfavorable weather. We discuss the possibility that the trade-off between degree of polyandry and life span when singly mated may affect the maintenance of genetic variability in female mating frequency in this species. Possible reasons for these different reproductive strategies are discussed.