Who determines the timing of inflorescence closure of a sexual dandelion? Pollen donors versus recipients

Male–male competition for mating or fertilization opportunities may in theory select for male manipulative adaptation that can harm males’ mates, leading to sexual conflict. Evolutionary theory predicts that selection will favor the manipulation by pollen of the duration of its recipients’ receptivity. However, there is insufficient evidence to show that pollen can exert effects on the duration of receptivity, a prerequisite for the evolution of pollen manipulative adaptation. Using a sexual diploid dandelion, Taraxacum japonicum, we conducted hand pollination experiments within and between populations to examine the effects of pollen on the timing of inflorescence (flower head) closure. We also examined the potential fitness consequences to the pollen recipients by field observation of seed production in populations with different inflorescence closure timing. Within-population experiments showed that pollination induced inflorescence closure even when some of the florets in the inflorescence were not yet pollinated with compatible pollen. Furthermore, between-population crosses revealed that pollen donors, recipients, and their interaction all influenced the timing of inflorescence closure. Different populations differed in the timing of inflorescence closure, which could affect the availability to the recipients of pollen for fertilization and thereby seed production. However, there were no significant differences in the rates of natural seed production in these populations. Our results demonstrate that pollen donors, as well as recipients, contribute to the duration of floral receptivity. We discuss the implications of our findings to the evolutionary theory of plant reproduction.