Abstract:

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.

Key words: distyly, elevation, pollen transfer efficiency, pollinator shift, Primula nivalis, self‐compatibility