Abstract:

The fundamental sexual condition of the vast majority of flowering plant species is hermaphroditism. Hermaphroditic individuals both receive and disperse pollen and may ultimately function as both maternal and paternal parents to the next generation of individuals. Such dual sex roles can result in conflicts and compromise the parental roles of plants during pollination and mating. Our aim in this review is to introduce the key concepts and various forms of sexual interference in flowering plants. Sexual interference can potentially take several distinct forms with contrasting reproductive consequences and has been recognized as occurring within flowers and between flowers. Intra-floral interference includes physical interference between sex functions, pollen clogging, and ovule discounting, while inter-floral interference refers to geitonogamous pollen discounting. The adaptive significance of floral diversity such as dichogamy, herkogamy, unisexuality, and self-incompatibility has largely been regarded in the literature as resulting only from selection to avoid selfing and the harmful effects of inbreeding, but without regard to the possibly important role that sexual interference has played. We review the limited experimental evidence for interference between sex functions and evaluate the hypothesis that some floral adaptations may serve an alternative function in reducing mating costs. In a broader sense, selfing also may be regarded as a form of sexual interference, or more specifically, male function (pollen dispersal) interfering with female function (seed production). Through imaginative experiments involving floral manipulations, it is possible to evaluate various forms of sexual interference in plants and their potential ecological and evolutionary significance.

Key words: Sexual interference, Selfing avoidance, Inbreeding depression, Co-sexuality