Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015 Lausanne, Switzerland.
Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015 Lausanne, Switzerland.
Curr Biol. 2021 Mar 22;31(6):1277-1283.e5. doi: 10.1016/j.cub.2020.12.028. Epub 2021 Jan 19.
Evolutionary transitions from hermaphroditism to dioecy have been common in flowering plants, but recent analysis also points to frequent reversions from dioecy to hermaphroditism. Here, we use experimental evolution to expose a mechanism for such reversions, validating an explanation for the scattered phylogenetic distribution of dioecy. We removed males from dioecious populations of the wind-pollinated plant Mercurialis annua and allowed natural selection to act on the remaining females that occasionally produced male flowers; such "leaky" sex expression is common in both males and females of dioecious plants. Over the course of four generations, females evolved a 23-fold increase in average male flower production. This phenotypic masculinization of females coincided with the evolution of partial self-fertilization, high average seed set in the continued absence of males, and a capacity to sire progeny when males were re-introduced into their populations. Our study thus validates a mechanism for the rapid dissolution of dioecy and the evolution of functional hermaphroditism under conditions that may frequently occur during periods of low population density, repeated colonization, or range expansion. Our results illustrate the power of natural selection, acting in replicated experimental populations, to bring about transitions in the mating behavior of plants.
雌雄同体到雌雄异体的进化转变在有花植物中很常见，但最近的分析也指出雌雄异体向雌雄同体的频繁逆转。在这里，我们使用实验进化来揭示这种逆转的机制，验证了雌雄异体在分散的系统发育分布中的解释。我们从风媒植物毛蕊花的雌雄异株种群中去除雄性，并允许自然选择作用于偶尔产生雄性花的剩余雌性；这种“渗漏”的性别表达在雌雄异株植物的雄性和雌性中都很常见。在四代的过程中，雌性的平均雄性花产量增加了 23 倍。这种雌性表型雄性化与部分自交的进化、在持续没有雄性的情况下平均种子结实率高以及当雄性重新引入其种群时产生后代的能力相一致。因此，我们的研究验证了在种群密度低、反复殖民或范围扩张等条件下，快速解散雌雄异体和进化功能雌雄同体的机制。我们的结果说明了自然选择在复制的实验种群中的力量，能够引起植物交配行为的转变。
