Soininen Jaakko O S, Kytöviita Minna-Maarit
Department of Biological and Environmental Sciences, Faculty of Mathematics and Science University of Jyväskylä Jyväskylä Finland.
Ecol Evol. 2022 Dec 28;12(12):e9670. doi: 10.1002/ece3.9670. eCollection 2022 Dec.
Sexual dimorphism is expressed as different morphologies between the sexes of a species. Dimorphism is pronounced in gynodioecious populations which consist of female and hermaphrodite individuals. The small size of female flowers in gynodioecious species is often explained by resource re-allocation to seed production instead of large flowers. However, pollinator attraction is critical to female fitness, and factors other than resource savings are needed to explain the small size of female flowers. We hypothesized that the floral size dimorphism in the perennial gynodioecious (L.) is adaptive in terms of pollination. To test this "pollination hypothesis," we video recorded the small female and large hermaphrodite flowers. We parameterized floral visitor behavior when visiting a flower and calculated pollination probabilities by a floral visitor as the probability of touching anther and stigma with the same body part. Pollination probability differed in terms of flower sex and pollinator species. Bumblebees had the highest pollination probability. The small female flowers were more likely to receive pollen via several pollinator groups than the large hermaphrodite flowers. The pollen display of hermaphrodites matched poorly with the stigma display of hermaphrodites, but well with that of females. Although the small size of female flowers is commonly explained by resource re-allocation, we show that sexual dimorphism in flower size may increase the main reproductive functions of the females and hermaphrodites. Dimorphism increases pollination probability in females and fathering probability of the hermaphrodites likely driving populations towards dioecy.
性二态性表现为一个物种两性之间的不同形态。在由雌性和雌雄同体个体组成的雌全异株种群中，二态性很明显。雌全异株物种中雌花的小花型通常被解释为资源重新分配用于种子生产而非大花。然而，传粉者吸引对雌性适合度至关重要，需要资源节省以外的因素来解释雌花的小花型。我们假设多年生雌全异株（L.）的花大小二态性在授粉方面是适应性的。为了检验这个“授粉假说”，我们对小的雌花和大的雌雄同体花进行了录像。我们对访花时传粉者的行为进行参数化，并计算传粉者访花时接触花药和柱头的概率作为授粉概率。授粉概率因花的性别和传粉者种类而异。熊蜂的授粉概率最高。与大的雌雄同体花相比，小的雌花更有可能通过几个传粉者群体接受花粉。雌雄同体花展示的花粉与雌雄同体花展示的柱头匹配度较差，但与雌花的匹配度较好。尽管雌花的小花型通常用资源重新分配来解释，但我们表明花大小的性二态性可能会增加雌性和雌雄同体的主要生殖功能。二态性增加了雌性的授粉概率和雌雄同体的父本概率，可能会推动种群向雌雄异株发展。
