Greater number of pollen donors improves female reproductive success but not progeny vigour in Allium stellatum

Plant-pollinator interactions affect the quantity and identity of pollen delivered to stigmas, influencing plant genetics and fitness. Here, we test the pollen competition hypothesis, which predicts that competition among pollen grains yields higher-quality offspring, by hand-pollinating Allium stellatum with pollen from one, two, or three donors while controlling pollen load size. We germinated seeds and assessed seed and seedling traits using generalised linear mixed-effects models. We found that flowers that received pollen loads with a greater number of donors had slower growing seedlings but also had a greater proportion of seeds that successfully germinated. These results provide mixed support for the pollen competition hypothesis, in that greater donor diversity leads to higher female reproductive success, but with a possible trade-off in progeny vigour. Pollen donor diversity thus affects reproductive outcomes and should be considered when examining how pollinators influence plant population dynamics.