1. Additional factors relevant to dispersal are necessary to establish a general theory that can explain the sex-biased dispersal pattern of most taxa. The present study evaluated the influence of pre-dispersal copulation on the evolution of sex-biased dispersal. The influence of fluctuating environment, population size and dispersal cost were also analysed.
2. The simulation models were designed on the basis of the life history of Pieris rapae crucivora, in which female butterflies disperse among local habitats after copulation although male butterflies remain in the natal habitat. In the first model, where females always copulate before dispersal, the evolution of female-biased dispersal was facilitated by the fluctuating environment, but was suppressed by the stable environment. However, the fluctuating environment also suppressed the sex-biased dispersal in the second model where female dispersers always copulate after dispersal. Thus, the interaction between the pre-dispersal copulation and the fluctuating environment is a sufficient condition for the evolution of sex-biased dispersal.
3. The present study is the first report to reveal the important influence of pre-dispersal copulation on the evolution of sex-biased dispersal. In addition, the sexual difference in dispersal pattern increased with the increase of local population size and the decrease of dispersal cost.