地果花粉供应格局成因和适生区分析

Linking the pollen supply patterns of Ficus tikoua to its potential suitable areas and key environmental factors

被子植物的性别表达与分配具有环境依赖性,使其性器官和雌雄功能在不同环境中趋于合理。地果雄果的花药胚珠比在不同地域间存在极大的变幅,同时呈现出不同的雄花分布格局,苞片口型(OS型)的花药胚珠比显著低于果腔散布型(SS型)。基于地果的339个实际分布点,使用最大熵模型模拟不同雄花分布类型地果的适生区,并对各适生区的环境贡献因子、区域间扩散的环境限制因子进行分析,探究地果雄花分布类型和花粉供应的地域分布格局成因。结果显示,OS型、SS型对应着不同的适生区,前者主要分布在四川盆地、后者主要分布在横断山区-云南高原、而贵州高原为多种类型的共存。各类型的环境条件有显著差异,OS型分布于低海拔、最冷月极端低温较低、温度季节变化明显的区域,而SS型分布于高海拔、强太阳辐射、温度季节变化较小的区域。环境条件的差异限制了地果在不同区域间的扩散,同时影响着地果的繁殖物候、传粉小蜂的种群动态等,这可能是地果性别分配策略变化的原因。

Plastic sex expression and allocation is common in angiosperm. Many plant species adjust their relative allocation to male and female organs in response to the environmental conditions in order to optimize sex functions in different environments. Large variation in anther-to-ovule ratios is presented among the natural populations of Ficus tikoua in the Southwest China. And it is associated with differing distributions of male flowers in the figs. Three male flower distributions occur, namely concentrated around ostiole(OS type), scattered throughout the fig cavity(SS type), and intermediate type(IS type). The anther-to-ovule ratios of OS type were significantly higher than those of SS type. We employed a maximum entropy model to simulate the potential suitable areas of F. tikoua based on 339 documented distribution sites. The key environmental factors contributing to the regional distribution of different plant phenotypes and restricting the expansion of the plant among regions were assessed. The distribution of the three phenotypes were largely allopatric, with OS type centered on Sichuan Basin, SS type concentrated on Hengduan Mountains-Yunnan Plateau, and co-occurrence on Guizhou Plateau. The environmental conditions associated with phenotype were different. OS type was associated with lower altitude, lower minimum temperature of the coldest month, and greater temperature seasonality. SS type was linked to higher altitude, stronger solar radiation, and smaller temperature seasonality. The different environmental conditions in each distribution region restricted cross-region expansion, brought about the variation of flower phenology of the plant and the population dynamics of its pollinating fig wasps, which might contribute to the divergence of sex allocation strategies of F. tikoua.