Ohya Itsuki, Nanami Satoshi, Itoh Akira
Graduate School of Science Osaka City University Osaka Japan.
Ecol Evol. 2017 Jun 15;7(15):5660-5668. doi: 10.1002/ece3.3117. eCollection 2017 Aug.
The reproductive capacities of dioecious plant species may be limited by severe pollen limitation and narrow seed shadows for the two reasons. First, they are unable to self-pollinate, and seed production occurs only with pollinator movement from males to females. Second, only 50% of the individuals in populations contribute to seed production. Despite these handicaps, dioecious plants maintain their populations in plant communities with cooccurring cosexual plants, and no substantial difference in population growth rates has been found between dioecious and cosexual plants. Hence, dioecious plants are thought to mitigate these disadvantages by adopting ecological traits, such as insect pollination, animal-dispersed fleshy fruits, and precocious flowering. We studied the relationship between flowering and plant size in 30 woody species with different sex expressions, leaf habits, fruit types, and maximum plant sizes. The study site was located in an evergreen broad-leaved forest on the island of Honshu, Japan. A phylogenetic linear regression model showed that dioecious species tended to mature at smaller sizes than did cosexual taxa. At the population level, given equal plant densities and reproductive efforts, the precocity of dioecious plants could serve as one of the factors that mitigate the limitations of pollen and seed-shadow handicaps by increasing the density of reproductive individuals in the population. At the individual level, smaller size of onset of flowering may play a role in enhancing reproductive success over a lifetime by increasing reproductive opportunities. We discussed the possible effect of the relationship between precocity and some ecological traits of dioecious plants, such as small flowers pollinated by unspecialized insects, fleshy fruit dispersed by animals, and their preferential occurrence in the tropics and in island habitats. The universality of precocity among dioecious plants should be investigated in diverse plant communities. Such studies will increase our understanding of the evolution of plant breeding systems.
由于两个原因，雌雄异株植物物种的繁殖能力可能会受到严重的花粉限制和狭窄的种子传播范围的限制。首先，它们不能自花授粉，只有在传粉者从雄性植株移动到雌性植株时才会产生种子。其次，种群中只有50%的个体参与种子生产。尽管存在这些不利因素，雌雄异株植物在与共存的两性植物的植物群落中仍能维持其种群数量，并且在雌雄异株植物和两性植物之间未发现种群增长率有实质性差异。因此，人们认为雌雄异株植物通过采用生态特征来减轻这些不利因素，例如昆虫授粉、动物传播的肉质果实和早熟开花。我们研究了30种具有不同性别表达、叶习性、果实类型和最大植株大小的木本植物的开花与植株大小之间的关系。研究地点位于日本本州岛的一片常绿阔叶林。系统发育线性回归模型表明，雌雄异株物种往往比两性分类群在较小的植株大小时成熟。在种群水平上，在植物密度和繁殖努力相同的情况下，雌雄异株植物的早熟可以作为通过增加种群中繁殖个体的密度来减轻花粉和种子传播范围限制的因素之一。在个体水平上，较小的开花起始植株大小可能通过增加繁殖机会在提高一生的繁殖成功率方面发挥作用。我们讨论了早熟与雌雄异株植物的一些生态特征之间关系的可能影响，例如由非专门昆虫授粉的小花、由动物传播的肉质果实，以及它们在热带地区和岛屿栖息地的优先出现。应该在不同的植物群落中研究雌雄异株植物中早熟现象的普遍性。此类研究将增进我们对植物繁殖系统进化的理解。
