Do seed dispersal strategies reflect adaptation to environmental variability?

Dispersal is one of the primary mechanisms by which organisms adapt to spatial and temporal variation in the environment. Theory predicts that increasing spatiotemporal variation drives selection for offspring dispersal away from their natal habitat and one another. However, due to inherent difficulties in measuring dispersal in plant systems, there are few empirical tests of the extent to which this hypothesis can explain variation in seed dispersal strategies. In this study, we characterized and compared the dispersal patterns of three closely related plant species that segregate across gradients in spatiotemporal variation in seasonal wetlands. We tracked individual seeds as they dispersed in their natural habitats to measure seed dispersal distance (the distance travelled from the maternal plant) and inter-seed spread (distances between dispersed seeds) and to identify the plant traits causing within-species variation in seed dispersal. We also evaluated the seed traits causing within-species variation in seed flight distance and terminal velocity in a wind tunnel and a drop tube, respectively. We found that average seed dispersal distance was lowest in the species that occupies the most spatiotemporally variable habitat, contradicting our predictions; however, inter-seed spread was lowest in the species from the least variable habitat, which aligned with our expectations. The maternal plant and seed traits explaining intraspecific variation in seed dispersal varied among species as well as the method used to measure dispersal potential. Two traits had non-intuitive effects on dispersal, including pappus size, which reduced seed flight distance in two of the focal taxa. Overall, our results indicate that the differences we detected in seed dispersal among three closely related plant taxa can be only partially explained by current patterns of environmental variability in their respective habitats and that the traits driving within-species variation in seed dispersal can evolve rapidly and change with the environmental context in which they are measured. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Dispersal is an important mechanism for organisms to adapt to environmental variation. This study tracked the dispersal patterns of three plant species in their natural habitats and identified the plant traits causing variation in seed dispersal. The results showed that average seed dispersal distance was inconsistent with the variation in habitat, while the minimum inter-seed distance aligned with the minimum habitat variation.