Chen Kai-Hsiu, Pannell John R
Department of Ecology and Evolution, University of Lausanne, Biophore Building, 1015, Lausanne, Switzerland.
New Phytol. 2025 Jul 6. doi: 10.1111/nph.70356.
The evolution of dioecy from hermaphroditism is widely thought to be a response to disruptive selection favoring males and females, driven by advantages of inbreeding avoidance, sexual specialization, or both. It has hitherto been difficult to uncouple the importance of these two hypotheses. We use phenotypes produced by experimental evolution to test the inbreeding avoidance hypothesis in populations from which sexual specialization can be effectively ruled out. We estimate the selfing rate and the shape of fitness gain curves under scenarios with and without inbreeding depression in experimental populations of wind-pollinated Mercurialis annua with high variation in sex allocation. Our results confirm a phenotypic trade-off between male and female allocation in M. annua. Individual selfing rates increased with pollen production. This dependence led to strong disruptive selection on sex allocation due to its interaction with the mating system under the scenario of high inbreeding depression, especially for plants of medium and large sizes. Taken together, our results demonstrate that inbreeding avoidance on its own can lead to disruptive selection on sex allocation, favoring the selection and maintenance of dioecy under wind pollination without associated benefits of sexual specialization.
雌雄异株从雌雄同体进化而来，普遍被认为是对有利于雄性和雌性的分裂选择的一种响应，这种选择由避免近亲繁殖、性别特化或两者兼具的优势驱动。迄今为止，很难区分这两种假说的重要性。我们利用实验进化产生的表型，在可以有效排除性别特化的种群中检验避免近亲繁殖假说。我们估计了在有近亲繁殖衰退和没有近亲繁殖衰退的情况下，风媒授粉的一年生山靛实验种群中性分配高度可变时的自交率和适合度增加曲线的形状。我们的结果证实了一年生山靛在雄性和雌性分配之间存在表型权衡。个体自交率随花粉产量增加。在近亲繁殖衰退程度高的情况下，由于这种依赖性与交配系统的相互作用，导致了对性分配的强烈分裂选择，特别是对于中型和大型植株。综上所述，我们的结果表明，仅避免近亲繁殖就可导致对性分配的分裂选择，有利于在风媒授粉下选择和维持雌雄异株，而无需性别特化带来的相关益处。
