Phenotypic variation in an invasive weed across multiple common gardens

Background/Question/Methods

What enables a plant species to become invasive? Ecological and evolutionary mechanisms predict different modes of invasion success. We investigate phenotypic changes that distinguish successful invaders from con-specifics from their native range in the invasive weed, Centaurea diffusa. We examine phenotypic differences between populations from the native and invaded ranges, using common garden experiments to test for resource allocation trade-offs by comparing growth rate and fecundity in the presence or absence of experimentally applied stresses. Results will indicate whether invasive populations of C. diffusa have higher growth rates than native populations, and if growth rate is correlated with stress tolerance. Colautti et al, 2008, suggest that such common gardens, conducted in a single location, are insufficient to address what phenotypic differences exist between native and introduced individuals. We therefore conducted multiple common gardens to look at early life history differences between native and invasive C. diffusa. These include a greenhouse common garden using field collected seed from 50 populations across the native and invasive range, a smaller greenhouse common garden using greenhouse produced seed to control for maternal effects, and a field common garden conducted in the naturalized range of C. diffusa.

Results/Conclusions

Data from all three common gardens experiments indicate that invasive individuals grow larger and potentially have higher fitness than individuals from the native range across all three experimental environments, including preliminary results from a field experiment in the naturalized range of the species. The field experiment in particular suggests that phenotypic differences are also found when experiments are replicated in the non-invasive range. This will allow future interpretation of any genetic differences found between the native and invaded ranges (in ongoing and future genetic analyses). This consistent phenotypic divergence between the native and invasive ranges could indicate evolved differences which have allowed for invasion success in this species.