Does a lack of mating opportunities explain monandry in the green‐veined white butterfly ( Pieris napi )?

In the nuptial gift‐giving butterfly, Pieris napi, multiple mating corresponds to higher lifetime fecundity than monandry does. Yet, female mating frequency, which is genetically determined and heritable, varies from strict monandry to a high degree of polyandry. Polyandrous females are known to suffer from reduced longevity when denied the opportunity to mate according to their intrinsic mating frequency. Here we test if monandry is likely to be maintained due to a lack of mating opportunities in the wild. We also explore longitudinal variation in female mating frequency (i.e. lifetime number of matings) and remating rate (i.e. time interval between successive matings). The latter was explored by comparing the mating patterns of females with varying origins in a laboratory, and the former by comparing the mating frequencies of wild and laboratory females. We were able to reveal spatial variation in female mating frequency, with monandry being a clearly more common mating tactic in the north than in the south. However, we did not find direct evidence that either the maintenance of monandry or spatial variation in female mating frequency is promoted by a lack of mating opportunities. Still, our findings may have profound implications, since decreasing mating frequency towards the north generates spatial variation in the strength of sexual selection.