目的:Gynodiecy是一种罕见的性系统,其中两种性别(sensuLloyd,1980),女性和女性,共存。为了生存,雌性植物必须弥补它们缺乏的母性能力和雄性吸引力。在欧洲栗子(栗子)中,一棵交叉的树,自花授粉减少了同性个体的坐果,这是由于后期的自交不亲和和早期的近交抑郁。这种消极的性互动可以解释该物种中雌性的存在吗?
方法:我们研究了欧洲栗子野生种群的性别变异。此外,我们比较了水果组(鲜花的比例)和其他关键的女性健康成分以及性别之间的生殖分配。然后我们在共性树中进行了去雄实验,通过去除产生花蜜的可育雄性花序。我们还从雌树中去除不育但产生花蜜的雄性花序,作为一个控制。
结果:我们发现欧洲栗子野生雄性不育个体的比例差异很大。在实验区,每个性别的树都有相似的大小,花的密度,和毛刺设置,但是水果不同。从树枝或整个树木中去除产生花蜜的雄性花序会增加同性树的坐果,但不会增加雌性树的坐果。
结论:这些结果表明,自花授粉会损害同性树的坐果。雌树避免了这些问题,因为它们不产生花粉,但由于它们有益的雄性不育花序而继续吸引传粉者,导致比cosexuals高得多的水果。这表明,即使是异株植物也可以从停止自花授粉中受益,单性可以进化。
OBJECTIVE: Gynodioecy is a rare sexual system in which two genders (sensu Lloyd, 1980), cosexuals and females, coexist. To survive, female plants must compensate for their lack of siring capacity and male attractiveness. In European chestnut (Castanea sativa), an outcrossing tree, self-pollination reduces fruit set in cosexual individuals because of late-acting self-incompatibility and early inbreeding depression. Could this negative sexual interaction explain the presence of females in this species?
METHODS: We studied gender variation in wild populations of European chestnut. In addition, we compared fruit set (the proportion of flowers giving fruits) and other key female fitness components as well as reproductive allocation between genders. We then performed emasculation experiments in cosexual trees, by removing nectar-producing fertile male inflorescences. We also removed sterile but nectar-producing male inflorescences from female trees, as a control.
RESULTS: We found a highly variable proportion of male-sterile individuals in the wild in European chestnut. In the experimental plot, trees from each gender had similar size, flower density, and burr set, but different fruit set. Removing nectar-producing male inflorescences from branches or entire trees increased fruit set in cosexual but not in female trees.
CONCLUSIONS: These results show that self-pollination impairs fruit set in cosexual trees. Female trees avoid these problems as they do not produce pollen but continue to attract pollinators thanks to their rewarding male-sterile inflorescences, resulting in a much higher fruit set than in cosexuals. This demonstrates that even outcrossed plants can benefit from the cessation of self-pollination, to the point that unisexuality can evolve.