Comparison of genetic variation in native and non-native populations of the grass Andropogon virginicus

Background/Question/Methods

Are introduced, non-native populations more or less genetically variable than native populations? This is an important question for understanding the ecological and evolutionary potential of non-native populations and also for planning biocontrol. Introduced populations may be expected to be less variable because of the founder effect. Alternatively, if they are very successful and are spreading widely, they may be expected to be more genetically variable, allowing them to exploit a wider range of environments. We examined genetic variation in native and non-native populations of Andropogon virginicus(broomsedge), a grass that is common and native in old-fields of the eastern U.S., introduced and naturalizing in mesic habitats of the Central Valley of California, and introduced and widely invasive in the Hawaiian Islands, notably in Hawaii Volcanoes National Park. We conducted  PCR using ISSR primers on 20 individuals each in 3-6 populations from each of the regions. We extracted DNA with DNeasy spin columns by Qiagen, from greenhouse plants grown from field-collected seed. Every test plant had a different seed mother. We calculated percent polymorphism and Nei’s gene diversity for each population, using methods for dominant markers. 

Results/Conclusions

Native A. virginicus populations exhibited, on average, somewhat higher percent polymorphism than the non-native populations (means: Native, 48.6%; California, 35.4%, Hawaii 38.9%), and included the population with the highest value (66.7%). The lowest value was in California (25%). However, ANOVA did not detect significant variation among the regions (P=0.11). The gene diversity results showed that populations from California were, on average, somewhat less genetically variable than the others (means: California, 0.09; Hawaii, 0.13; native, 0.12), but the regions were not significantly different (P=0.18). These results suggest the possibility that Californian populations of A. virginicus are generally less diverse than other populations (addition of more ISSR markers and populations will provide more information). This may be due to a founder effect but additionally, in the seasonally dry Central Valley, the perennial A. virginicus is restricted to lakeshores, riparian corridors, seeps, etc. This restriction may have acted to select for a narrow range of genotypes. The plant is found in a much wider range of habitats where native. In the remote Pacific islands of Hawaii, where a strong founder effect might be expected, it grows in variable niches that range from very xeric lava flows resembling asphalt to pastures and submontane forests.