PS 36-75
Rapid evolution of dispersal-related traits during range expansion of an invasive vine Mikania Micrantha H.B.K.
Plant invasions serve as a unique opportunity to explore evolutionary changes in life-history traits during range expansion. Among multiple traits, dispersal ability likely has the most critical impact on population spread. Both theoretical and empirical studies suggest that dispersal ability is favored towards range edge. However, the contribution of genetic differentiation and phenotypic plasticity to this process is not yet clear. Here we aimed to explore (1) whether dispersal traits are more developed in margin vs. core populations, (2) if so, whether differences are due to genetic differences. Mikania micrantha H.B.K. was used in our study, one of the top 10 worst weeds worldwide with well-documented invasion history in Guangdong, China. We collected seeds from 36 field populations across Guangdong. Sixteen typical populations out of these 36 were used in a common garden experiment. We measured seed mass, pappus radius, and plume loading, to represent dispersal potential, of seeds from both field and common garden. We also recorded the road distance to core population, field population area and percent cover for each field population. We investigated how dispersal-related traits respond to these factors.
Results/Conclusions
In field populations, both plume loading and seed mass significantly decreased along invasion route, whereas pappus radius did not correlate with any of the three variables. This result suggests dispersal potential is more developed in margin populations, meanwhile the increase of dispersal rate likely came with seedlings fitness cost. In common garden populations, seed mass and pappus radius did not show significant correlations with any factors. However, plume loading exhibited significant quadratic correlation with field percent cover. Populations from medium percent cover showed higher dispersal potential than those from high and low percent cover, suggesting that phenotypic differences among populations were likely genetic-based. Furthermore, the rebound of dispersal ability in highly competitive sites suggested that the evolutionary process was likely partly driven by intraspecific density. Together, our results suggest that dispersal ability of M. micrantha populations are selectively favored during rapid expansion and the evolution of dispersal traits is influenced by intraspecific competition intensity. In light of that more and more plant species are under spatial nonequilibirum due to climate change, our study can serve to provide hints to the fate of spatially fluctuant populations.