Trade-off between dispersal traits in a heterocarpic plant across its invasion route

Dispersal ability can vary across plant species or populations, such as among core compared to leading populations of invasive plants. However, in heterocarpic plants, which produce propagules with varying dispersal abilities, dispersal potential can also increase via investment in the proportion of dispersing morphs (termed dispersal rate). Nevertheless, very little is known about the interplay between investment in dispersing structures vs. dispersal rate or how each is affected by varying environmental pressures.

Methods

This study examined the interplay between investment in dispersing structures and dispersal rate across the invasion route of the heterocarpic plant Heterotheca subaxillaris. H. subaxillaris's capitula were collected from eight populations along its invasion route in the Eastern Mediterranean coastal plain. The dispersal ability of dispersing pappus-bearing achenes was measured as the ratio between their pappus width and biomass. The dispersal rate was calculated as the ratio between the number of dispersing achenes and total achenes per capitulum. 

Key Results 

The dispersal ability of the dispersing achenes and dispersal rate were found to be negatively correlated across H. subaxillaris' populations, with a greater investment in pappus length in populations at the leading edge of the invasion compared to a greater number of dispersing achenes in core populations.

Conclusions 

Our results suggest a trade-off might exist between dispersal ability and dispersal rate, which could change along the invasion route of heterocarpic plants such as H. subaxillaris and contribute to their invasive success. This study highlights the importance of examining both dispersal traits when studying the dispersal potential of heterocarpic species.