Genetic diversity in native and invasive populations of an annual herb

Background/Question/Methods

Exotic invasive species pose a great threat to global biodiversity and can incur substantial economic costs. While not all introduced species become invasive, those that do must be able to proliferate in novel habitats. Thus, invasiveness may be linked to the adaptive potential of introduced populations; as such, the effects of the introduction/colonization process on the levels and distribution of genetic diversity introduced in invasion scenarios may be integral to the success of an introduced population. Here, we report on a comparative biogeographical study of genetic diversity in the annual plant Geranium carolinianum across its native (N. America) and invasive (E. Asia) ranges. Individuals were sampled from 26 US populations and 24 populations in eastern China and genotyped at 30 allozyme loci. Levels and patterns of genetic diversity were compared between countries to assess whether invasive populations have reduced genetic diversity relative to their native counterparts.

Results/Conclusions

Genetic analyses demonstrate significant genetic structure among populations of G. carolinianum, both globally and within regions (native or invasive). Regional comparisons show low levels of genetic differentiation between the US and China, but Chinese populations are significantly less diverse, with less genetic structure than in the US. This provides evidence for weak founder effects in invasive populations, but higher genetic admixture relative to native populations. Patterns of genetic diversity among US populations suggest that colonization-extinction dynamics are structuring diversity in the native range. This model is appropriate for G. carolinianum, as this species typically occupies frequently disturbed, degraded roadside habitats, and likely experiences high rates of local colonization and extinction as well as human-mediated long-distance dispersal.

A thorough analysis of genetic diversity in the native range provides insight into the natural history of the species as well as a baseline for comparison with invasive populations. Knowledge of genetic diversity in Chin provides essential information on both its introduction history as well as its evolutionary potential. Such information can be useful for developing control and risk-assessment programs.