Abstract:

Aims: Pollinator-mediated variation in floral morphology is mostly observed in specialized pollination systems. For widely distributed plants that rely on generalized pollination, it remains unclear how their morphological traits and pollinator assemblages vary along geographical gradients, and their correlations with latitude, longitude and altitude. Our preliminary study has revealed that Dipsacus asper (Dipsacaceae) is widely distributed in southwestern China and exhibits a typical generalized pollination system, making it an ideal material for investigating this question. 

Methods: In this study, we took D. asper as the experimental material and conducted field investigations across 13 wild populations concentrated in Hubei, Sichuan, Yunnan, and Guizhou provinces. We measured the morphological traits of the plants, compared the morphological characteristics among populations, and calculated the coefficients of variation (CV) within and between populations. Additionally, we observed and recorded the pollinator types in each population and calculated their visitation frequencies. We also measured the body characteristics of the main pollinator bumblebees. Finally, we quantified natural seed set of D. asper across the different populations. 

Results: The results indicate significant variation in the morphological traits of D. asper across different populations. Specifically, the CV were high for leaf and stem traits, whereas inflorescence size showed low variation. D. asper plants from Xiaojin, Jianshi, Yanyuan and Xishui populations exhibited larger inflorescences compared to other populations. The primary pollinators of D. asper included Bombus, Apis, Eristalis and Lepidoptera, with bees serving as key pollinators. Both pollinator composition and visitation frequency varied markedly among populations. The larger-bodied bumblebees as main pollinator for plant in Xiaojin, Jianshi, Yanyuan and Xishui populations. There was no significant correlation between the corolla tube length of D. asper and the proboscis length of widely distributed Bombus friseanus. Plant height, stem, leaf, and inflorescence size of D. asper, as well as the morphological characters of B. friseanus, decreased with increasing elevation and they also varied with longitude and latitude. Plant height and the proboscis length of B. friseanus increased with increasing longitude, while the sizes of stems, leaves, inflorescences, and the abdomen of B. friseanus decreased with increasing longitude. Leaf size, inflorescence size, the thickness of the head and thorax, and the abdomen of B. friseanus increased with increasing latitude, whereas the proboscis length of B. friseanus decreased with increasing latitude. Additionally, the natural seed set of D. asper with different geographical distributions showed an increasing trend with the increase of longitude, a significant decreasing trend with the increase of latitude, and a significant increasing trend with the increase of altitude. 

Conclusion: The morphological traits and its pollinator diversity of widely distributed plant species exhibit significant variation along geographical gradients. This variation may be resulted from the combined effects of plant-pollinator interactions and abiotic environmental factors. Across different geographical environments, plants ensure their reproductive success by adapting floral morphology and utilizing diverse pollinators.

Key words: geographical variation, Dipsacus asper, morphological characters, pollinators, reproductive success