The impact of pollinator functional traits on pollination effectiveness is shaped by floral morphs in distylous plant species

Insect pollinators provide essential ecosystem services, and pollination effectiveness is a key factor in evaluating the relative importance of different insect species. While single-visit deposition (SVD) of pollen on virgin stigmas by insects is usually used to measure pollination effectiveness, how SVD is correlated with species behavioural and morphological traits is poorly understood for different floral morphs. Here, we used distylous common buckwheat (Fagopyrum esculentum Moench) as a model to understand the relationship between SVD and pollen load, key morphological and behavioural traits of pollinators, and how such relationships differ between different floral morphs. We quantified SVD for 16 insect species and measured the body length, proboscis length, pollen load on different parts of the body, and average visit duration for each species. The results showed that SVD is generally positively correlated with pollen load. SVD is significantly positively associated with species body length but negatively associated with proboscis length for thrum flowers but not for pin flowers. Similarly, positive relationships between SVD and visit duration were observed for thrum flowers, but no significant relationship was observed for pin flowers, while flower visit duration was negatively associated with proboscis length. This study also indicates trait-matching between flowers and pollinators, i.e. the short proboscis length is well matched with the short stamen (pin flower) and short style (thrum flower) and hence promotes compatible pollen deposition on thrum flowers. Our study suggests that morphological trait-matching between flowers and pollinators influences the outcome of plant–pollinator interactions, contributing to variations in pollination effectiveness among different pollinators.