Background/Question/Methods Within their introduced range, invasive plants face varying selection pressures at their expansion front compared to core populations. For example, dispersal ability has been suggested to increase in populations at the expansion front. However, some plant species have a dual dispersal strategy and produce both non-dispersing and dispersing fruit morphs. In these heterocarpic species, the production of non-dispersing fruits, which germinate close to the mother plant, can mitigate the risks of dispersal in uncertain environments and might therefore provide an advantage at the invasion front. However, changes in dispersal potential of heterocarpic species along the invasion front has not been tested thus far. Here, we examined differences in dispersal potential among populations of the invasive heterocarpic species Heterotheca subaxillaris (Asteraceae), along its invasion range in the coastal sand dunes of Israel. We collected flower heads of H. subaxillaris from nine populations along its invasion range (20 individuals per population) and compared the weight and number of non-dispersing vs. wind-dispersed achenes (fruits) per each flower head. Results/Conclusions Non-dispersing achenes of H. subaxillaris were found to be generally lighter than wind-dispersed achenes, and this difference did not change between populations along the invasion range. In contrast, while more wind-dispersed achenes were generally produced per flower head, their proportion decreased in plants from the invasion front compared to core populations. These results suggest that in H. subaxillaris, populations at the invasion front might be selected for greater investment in achenes that disperse close to the mother plants, as the latter might provide sand stabilization and hence improved conditions for germination. These findings imply that heterocarpy might facilitate not only dispersal ability but also establishment at the invasion front and thus contribute to range expansion of invasive species.
