Graduate School of Human Development and Environment, Kobe University, Kobe, Japan.
Plant Biol (Stuttg). 2022 Mar;24(2):259-265. doi: 10.1111/plb.13383. Epub 2022 Jan 6.
Andromonoecy, the presence of perfect and staminate flowers in the same individual, has evolved repeatedly in angiosperms. The staminate flowers are generally smaller than the perfect flowers in species that produce staminate flowers plastically when resources are limited. The smaller staminate flowers are expected to be less attractive to pollinators and have reduced size-matching with pollinators than perfect flowers. We hypothesized that these potential disadvantages of staminate versus perfect flowers facilitate the evolution of sex-specific floral morphology, such as allometric relationship between flower size and male reproductive organ. We compared six floral morphology traits, pollen production, pollinator visits and pollen removal from anthers between staminate and perfect flowers in several natural Commelina communis populations. Nectarless and zygomorphic C. communis flowers have polymorphic stamens with attracting, feeding and pollinating anthers and were visited by diverse pollinators. Staminate flowers were significantly smaller than perfect flowers, despite a large overlap in size between sexes. The lengths of pollinating stamens did not differ between staminate and perfect flowers, and staminate flowers produced significantly more pollen. We observed significantly more pollinator visits to perfect flowers than to staminate flowers. By contrast, pollen removal from pollinating stamens was significantly higher in staminate flowers than in perfect flowers. There is sexual dimorphism in flower morphology in C. communis. Staminate flowers with smaller attraction organs, similar pollinating stamens and higher pollen production assure higher pollen donor success relative to perfect flowers. Our results suggest that the morphological changes in staminate flowers enhance pollination success, even with limited resources.
雌雄同株性，即同一植株同时存在完全花和雄花，在被子植物中多次进化。当资源有限时，产生雄花的物种中的雄花通常比完全花小。较小的雄花预计对传粉者的吸引力较小，与完全花相比，雄花花蕊大小匹配度降低。我们假设，与完全花相比，雄花的这些潜在劣势促进了性别特异性花形态的进化，例如花大小和雄性生殖器官之间的比例关系。我们比较了几个自然种群中，几种花形态特征、花粉产生、传粉者访问和花粉从花药中去除，涉及到雄花和完全花。无蜜和左右对称的鸭跖草花具有多态性雄蕊，具有吸引、喂食和授粉功能的花药，并被各种传粉者访问。尽管两性之间存在很大的大小重叠，但雄花明显小于完全花。授粉雄蕊的长度在雄花和完全花之间没有差异，而雄花产生的花粉明显更多。我们观察到，传粉者对完全花的访问明显多于雄花。相比之下，从授粉雄蕊中去除的花粉在雄花中明显高于完全花。鸭跖草存在花形态的性别二态性。具有较小吸引器官、相似授粉雄蕊和更高花粉产量的雄花，相对于完全花而言，保证了更高的花粉供体成功。我们的结果表明，即使资源有限，雄花的形态变化也能增强授粉成功。
