Sexual conflict in protandrous flowers and the evolution of gyndioecy

Sexual interference between male and female function in hermaphrodite plants is reduced by protandry. In environments with insufficient pollinator service, prolongation of male function owing to limited pollen removal could restrict the duration of female function lowering seed production. We provide evidence that this form of sexual conflict has played a role in the spread of females in gynodioecious populations of <i>Cyananthus delavayi</i> in the pollen-limited environments in which this subalpine species occurs. Using field experiments involving artificial pollen removal from the strongly protandrous flowers of hermaphrodites, we demonstrated a negative trade-off between male- and female-phase duration. Pollen removal at the beginning of anthesis resulted in hermaphrodite seed production matching that of females. In contrast, restricted pollen removal increased the duration of male function at the expense of female function lowering maternal fertility compared to females. This latter pattern was evident in five populations we investigated, with females experiencing a two-fold average seed fertility advantage compared to hermaphrodites. Gynodioecy often evolves from protandrous ancestors and pollen limitation is widespread in flowering plants suggesting that sexual conflict may play an unappreciated role in the evolution of this form of sexual dimorphism.