Patterns of genetic diversity in highly invasive species: Cogongrass (Imperata cylindrica) Expansion in the invaded range of the southern United States (US)
The spatial expansions of invasive organisms in the novel range are generally expected to follow an isolation-by-distance relationship (IBD) if the invasion is biologically driven; however, many invasions are facilitated anthropogenically. This research focused on the extant expansion patterns of cogongrass (Imperata cylindrica). Cogongrass is a widespread invasive species throughout the southern UnitedStates(US). Patterns of infestation vary among US states. Cogongrass is pyrogenic, and its invasion threatens softwood (Pinusspp.) plantations, a substantial economic market for this US region. Over 600 individuals were sampled from seven invaded US states, using ampliﬁed fragment length polymorphisms (AFLPs) to assess genetic diversity and population structure. We suspected that diﬀerences in historical management eﬀorts among US states inﬂuenced diﬀerences in genetic diversity and structure. We detected two genetic lineages at the highest level of analysis. One genetic lineage was locally restricted, whereas the other was found throughout the study region. Admixed individuals were found in all US states and consistently co-occurred with the dominant lineage, suggesting that secondary contact and hybridization may have facilitated expansion. The widespread prevalence of only one of the two detected genetic lineages suggests a primary genetic lineage responsible for on-going population expansion in the US.