Direct tracking of pollen with quantum dots reveals surprising uniformity in dispersal distance across 11 populations of an annual plant

Abstract

Premise: Pollen movement is a crucial component of dispersal in seed plants. Although pollen dispersal is well studied, methodological constraints have made it challenging to directly track pollen flow within multiple populations across landscapes. We labeled pollen with quantum dots, a new technique that overcomes past limitations, to evaluate the spatial scale of pollen dispersal and its relationship with conspecific density within 11 populations of Clarkia xantiana subsp. xantiana, a bee-pollinated annual plant. Methods: We used experimental arrays in two years to track pollen movement across distances of 5-35 m within nine populations and across distances of 10-70 m within two additional populations. We tested for distance decay of pollen dispersal, whether conspecific density modulated dispersal distance, and whether dispersal kernels varied among populations across an environmentally complex landscape. Results: Labeled pollen receipt did not decline with distance over 35 m within eight of nine populations or over 70 m within either of two populations. Pollen receipt increased with conspecific density. Overall, dispersal kernels were consistent across populations. Conclusions: The surprising uniformity in dispersal distance within different populations was likely influenced by low precipitation and plant density in our study years. This suggests that spatiotemporal variation in the abiotic environment substantially influences the extent of gene flow within and among populations.

Pollen as the link between floral phenotype and fitness

“…The development of new pollen-labeling techniques such as quantum dots has opened new opportunities for quantifying the fates of pollen grains after pollen placement onto a pollinator , but their empirical implementation has been relatively slow. We are convinced that such pollen-labeling methods will facilitate studies of pollen transfer (Kern et al, 2023) and the systemspecific performance-fitness relationships associated with pollen loss during transfer (Minnaar and Anderson, 2021). Detailed pollen tracking methods may also allow us to link pollination performance more closely to pollen performance and hence gain a more holistic understanding of when and why specific pollen grains are more competitively successful than others.…”

“…Besides landscape-scale effects of pollinator mobility, differences in pollinator foraging patterns and behavior may also affect small-scale pollen-transfer efficiency and siring success within populations Kern et al, 2023). In two studies in this issue, aspects of pollination efficiency were compared across different bee species.…”