What influences pollen dispersal in the clonal distylous Menyanthes trifoliata (Menyanthaceae)?

Background and aims – Habitat fragmentation may compromise population survival and decrease the ability to face environmental changes. Small and isolated populations in particular may suffer from disrupted pollination processes. However, a species’ response to fragmentation may vary according to life history traits. Understanding how pollen dispersal is shaped by population and life history traits such as mating system and clonal growth is therefore essential for assessing species’ response to fragmentation. Methods – We investigated pollen dispersal using fluorescent dyes in nine Belgian populations in two regions of the distylous insect-pollinated clonal herb Menyanthes trifoliata. We examined whether overall and legitimate (i.e. between-morph) dye dispersal patterns differed between morphs and regions, and whether they were influenced by population traits (size, area, plant density, morph ratio, co-flowering species) and individual plant traits (number of flowers). Key Results – No evidence of dye transfer between adjacent populations (distant from 1.3 to 11.8 km) was found, suggesting no or very restricted between-population pollen flow. Within-population dye dispersal followed a decaying, usually leptokurtic, distribution, with most dye deposition at short distances (80% at less than 1.9–49.1 m), and a maximum distance of 336.6 m. Pins and thrums as recipients or donors did not differ in dye dispersal. Legitimate dye dispersal was not less successful than overall dispersal despite spatial clumping of the morphs. The distribution was similar or simply shifted to longer distances. The proportion of dyed stigmas was positively related to flowering population size and within-population heterospecific floristic richness, and to the number of flowers when considering legitimate dye deposition at distances < 32 m. Conclusions – Our study highlights the effects of the spatial distance to dye source, population size and coflowering floral resources, i.e. population traits related to attractiveness to pollinators, on pollen dispersal patterns