植物花对称性与传粉系统密切相关, 花特征的变异性受到传粉者的选择作用。由于特化的传粉者对两侧对称的花的稳定选择, Berg假说认为两侧对称植物花大小的变异性比辐射对称植物的更低; 而且, 在传粉者的选择作用下花特征比植物营养特征明显有更低的变异性, 因为后者更易受环境影响。该文对青藏高原东部高山草甸植物群落的50种开花植物(包括19种两侧对称植物和31种辐射对称植物)的花和叶特征进行了测定和分析。结果表明不论是两侧对称植物还是辐射对称植物, 花大小的变异性都显著低于叶片大小的变异性, 表明传粉者对花施加的稳定选择有利于花的稳定性。但是, 辐射对称物种花大小的变异程度和两侧对称物种的相似, 即使在控制物种系统发育的影响后, 也没有发现显著的差异, 这与Berg假说不一致。高山生态系统中传粉者种类相对较少, 以熊蜂和蝇类为主, 传粉者的活动受局域气候环境影响较大, 因此传粉昆虫对植物花的选择作用强度可能有较大的变异性。

Aims Flower symmetry is closely related to pollination system and variations in flower traits are under the selection role of pollinators. Berg predicted that flower size varies much less in bilateral species than in radial species because of the stable and/or directional selection by pollinators, and that it should also show lower variability than vegetative organs which have relatively higher sensitivity to environments. We examined these so-called Berg’s hypotheses in an alpine meadow.
Methods By measuring the traits of flowers and leaves in 50 flowering plants in an alpine meadow in the eastern Qinghai-Xizang Plateau, we compared the coefficients of variations (CV) in flower size and leaf size between 31 radial and 19 bilateral species and also performed phylogenetically independent comparisons.
Important findings Our results were not completely consistent with the Berg’s hypotheses. The CV of flower size was significantly smaller than that of leaf size in both radial and bilateral species as predicted by Berg, indicating that pollinator-mediated stabilizing selection would benefit flower stability. But the CV of flower size did not differ between the bilateral and the radial species, which is inconsistent with the Berg’s hypothesis even if we controlled confounding effects of phylogenetic relatedness. The role of pollinators in alpine ecosystem where bumble bees and flies predominate is likely more affected by local climatic environments, which leads to considerable variability in the selection of pollinators on flowers.