Nguyen M T, Pannell J R
Department of Ecology and Evolution, University of Lausanne, 1015, Lausanne, Switzerland.
Heredity (Edinb). 2025 Jan;134(1):1-9. doi: 10.1038/s41437-024-00729-7. Epub 2024 Oct 14.
Trioecy, the co-existence of females, males and hermaphrodites, is a rare sexual system in plants that may be an intermediate state in transitions between hermaphroditism and dioecy. Previous models have identified pollen limitation as a necessary condition for the evolution of trioecy from hermaphroditism. In these models, the seed-production and pollen production of females and males relative to those of hermaphrodites, respectively, are compromised by self-fertilization by hermaphrodites under pollen- limitation. Here, we investigate the evolution of trioecy via the invasion of cytoplasmic male sterility (CMS) into androdioecious populations in which hermaphrodites co-occur with males and where the male determiner is linked to a (partial) fertility restorer. We show that the presence of males in a population renders invasion by CMS more difficult. However, the presence of males also facilitates the maintenance of trioecy even in the absence of pollen limitation by negative frequency-dependent selection, because males reduce the transmission of CMS by females by siring sons (which cannot transmit CMS). We discuss our results in light of empirical observations of trioecy in plants and its potential role in the evolution of dioecy.
三性花现象，即雌性、雄性和雌雄同体共存，是植物中一种罕见的性系统，可能是雌雄同体和雌雄异株之间转变的中间状态。先前的模型已将花粉限制确定为从雌雄同体进化出三性花现象的必要条件。在这些模型中，在花粉限制的情况下，雌雄同体的自花受精分别损害了雌性和雄性相对于雌雄同体的种子产量和花粉产量。在这里，我们通过细胞质雄性不育（CMS）侵入雄花两性花同株种群来研究三性花现象的进化，在这种种群中，雌雄同体与雄性共存，且雄性决定因子与一个（部分）育性恢复基因连锁。我们表明，种群中雄性的存在使CMS的侵入更加困难。然而，雄性的存在也通过负频率依赖选择促进了三性花现象的维持，即使在没有花粉限制的情况下也是如此，因为雄性通过产生儿子（不能传递CMS）减少了雌性对CMS的传递。我们根据对植物三性花现象的实证观察及其在雌雄异株进化中的潜在作用来讨论我们的结果。
