Who determines the timing of inflorescence closure of a sexual dandelion?: Pollen donors vs. 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, confirming that a prerequisite for sexually antagonistic adaptation is satisfied and suggesting manipulative adaptation of pollen or its donor. We discuss the implications of our findings to the evolutionary theory of plant reproduction.

从理论上来说，针对交配或受精机会的雄性间竞争，可能会选择出能够对其配偶造成伤害的雄性操控性适应，进而引发性冲突。进化理论预测，自然选择会倾向于青睐那些能够调控受体可受性时长的花粉操控策略。然而，目前尚无足够证据表明花粉能够对可受性时长产生影响——而这一效应正是花粉操控性适应演化的必要前提。本研究以有性生殖二倍体日本蒲公英（Taraxacum japonicum）为研究对象，在种群内部以及种群间开展人工授粉实验，以探究花粉对花序（花头）闭合时间的调控作用。同时，通过野外观察不同花序闭合时长种群的种子产量，我们还分析了花粉受体可能面临的适合度后果。种群内实验结果显示，即便花序内部分小花尚未接受亲和花粉授粉，人工授粉仍可诱导花序提前闭合。进一步的种群间杂交实验表明，花粉供体、受体以及二者的交互作用均会对花序闭合时间产生显著影响。不同种群的花序闭合时长存在差异，这可能会影响受体获取用于受精的花粉的可及性，进而影响种子产量。但本研究中，各野生种群的自然种子结籽率并未出现显著差异。本研究结果证实，花粉供体与受体共同决定了花部可受性的持续时长，满足了性拮抗适应演化的必要前提，同时提示花粉或其供体存在操控性适应。最后，我们就本研究发现对植物生殖进化理论的启示展开了讨论。