Pollinator shift and its influence on floral traits have been well documented to explain the diversity of angiosperms, but such effects are still less known at the intraspecific level, especially the responses of different morphs of distylous plants. We hypothesized that the pollen transfer efficiency would decrease if the pollinator shifted from a long-tongued to short-tongued insect across populations, and plants would evolve towards selfing in response to the stressed pollination environment. Given the gender specialization between flower morphs, the long styled (L-morph) plants would increase female reproduction. Our study showed that the short-tongued Bombus tianshanicus, the most-visit pollinator in high elevation populations of distylous Primula nivalis, was less efficient in pollen transfer than long-tongued Bombylius major. The plants evolved to promote selfing through reducing the anther–stigma separation and increasing intramorph self-compatibility. The hand pollination experiment showed that after intramorph selfing, the fruit set and seed set increased with increasing elevation. Moreover, anther and stigma were closer in the L-morph than in the short styled (S-morph) plants, and the L-morphs showed higher pollen transfer efficiency than the S-morphs. Along with increased self-compatibility, the fruit set and seed set of L-morph plants were significantly higher than those of S-morph plants. We described the pollinator shifts along an elevation gradient in a distylous plant and the response of plants by promoting selfing, which confirmed our hypothesis and supported the pollinator-shift model. Our study also highlighted the different response in self-compatibility between flower morphs.

中文翻译：

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传粉媒介沿海拔梯度的移动介导了异花报春花自花授粉的不同反应

传粉者转移及其对花性状的影响已被充分证明可以解释被子植物的多样性，但这种影响在种内水平上仍然鲜为人知，尤其是不同形态的二柱植物的反应。我们假设如果传粉者在种群中从长舌昆虫转变为短舌昆虫，花粉转移效率会降低，并且植物会因受胁迫的授粉环境而进化为自交。鉴于花型之间的性别特化，长型（L-型）植物会增加雌性繁殖。我们的研究表明，短舌熊蜂是雪花报春高海拔种群中访问量最大的传粉者。, 在花粉转移方面的效率低于长舌Bombylius major. 植物进化为通过减少花药柱头分离和增加形内自交亲和性来促进自交。人工授粉试验表明，形内自交后，坐果和结实率随海拔升高而增加。此外，L-morphs 的花药和柱头比短花型 (S-morph) 植物更接近，L-morphs 的花粉转移效率高于 S-morphs。随着自交亲和性的增加，L型植物的座果率和种子座率显着高于S型植物。我们描述了花序植物中传粉者沿海拔梯度的变化以及植物通过促进自交的反应，这证实了我们的假设并支持了传粉者转移模型。