Print PageBig bluestem is a dominant C4 grass distributed across a sharp precipitation gradient (400-1200 mm yr-1 from Kansas to Illinois) which has likely produced ecotypic variation in drought tolerance and potentially, local drought adaptation. A better understanding of ecotypic variation will help predict how this dominant species might respond to climate change and will inform restoration efforts of suitable populations sources current and future conditions. We investigated the link between phenotypic variation and genetic diversity by using reciprocal common gardens planted in Illinois, eastern Kansas (Manhattan), central Kansas (Hays), and western Kansas(Colby). , KS (to test ecotype tolerance limit into drier areas). At each site ecotypes from each region (each comprised of seed collected from four pristine populations in Hays, Manhattan, and Illinois) were reciprocally planted in replicate blocks with each plant growing singly and in replicated assembled seeded communities (16 m2 plots). We measured phenotypic variation in drought tolerance across ecotypes and sites. Because genetic diversity may be critical for predicting a species’ ability to adjust/adapt to climate change, we assessed genetic diversity and population differentiation using genome scans of Andropogon gerardii in the 12 source populations. also used in the reciprocal garden experiment.
Results/Conclusions
A strong phenotypic cline in drought tolerance of the three ecotypes was evident. The western-most ecotype (Hays) exhibited local adaptation to drought based on the reciprocal garden results. Establishment and cover in the seeded plots showed a significant ecotype (p<0.0001), site (p<0.0001) and interaction effect (p<0.0001). The Hays ecotype had disproportionate cover in western regions relative to the Illinois and Manhattan ecotypes (i.e., gene by environment interaction), indicating local adaptation to drought. Specifically, the Hays ecotype had 2-3 times the cover compared to other ecotypes in the Hays and Colby sites, respectively. We analyzed 412 plants (~20 plants per population) and identified 387 markers using 2 primer pairs. Several lines of evidence (i.e., neighbor joining trees, STRUCTURE and PCA analyses) support genetic differentiation and population structuring of ecotypes, with the greatest variability found within Illinois populations (92%). Further, PCA analyses showed 47% of the variation in axis one eigenvalue was explained by mean annual rainfall. Lastly, 11 ecotype-specific loci under diversifying selection were identified using BAYESCAN. In spite of the genetic differentiation found among ecotypes, ANOVA analyses partitioned the greatest genetic variation within populations (80%). This high, within-population genetic diversity may contribute to the resiliency of bluestem populations that experience environmental change, with implications for prairie restoration.
Results/Conclusions
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