Local adaptation is a fundamental phenomenon in evolutionary, conservation, and global climate change biology, with applications for restoration and climate adaptation. Local adaptation is defined as ecotypes from local populations outperforming non-local transplants. Our research deals with adaptive variation in drought tolerance and local adaptation of an ecologically dominant grass big bluestem Andropogon gerardii across the Great Plains’ grasslands. This grass represents as much as 70% of prairie biomass and is widely used in conservation plantings over ~ 5 million acres across the Great Plains. Because of the wide geographic distribution across a precipitation gradient (500-1200 mm/yr from western KS to IL, we expect intraspecific variation in A. gerardii in response to precipitation. Objectives are to 1) use reciprocal gardens to investigate ecotype differences in vegetative and reproductive traits, 2) characterize genetic divergence among ecotypes, and 3) identify outlier loci and potential candidate genes responsible for divergence. Three ecotypes (central KS, eastern KS, and Illinois) were reciprocally planted in Colby, Hays, and Manhattan, KS, and Carbondale, IL. We evaluated ecotypic differences in vegetative and reproductive features across sites, predicting ecotypes would perform best at “home”.
Results/Conclusions
The xeric Central KS ecotype shows traits consistent with drought tolerance and local adaptation—reduced canopy, short stature, and early flowering. PCA shows trait variation sorting along a longitudinal precipitation gradient. Morphology was correlated with seasonal mean precipitation and temperature, elevation, and size of precipitation events. We used Genotyping-by-Sequencing to identify 4,641 single nucleotide polymorphisms (SNPs). The IL ecotype existed as a distinct genetic group while the Kansas ecotypes showed admixture. Genetic outlier analysis identified 373 SNPs showing divergent selection. Of the top 1% of outliers, SNPs were primarily associated with seasonal diurnal temperature variation and seasonal precipitation. We identified a key candidate gene of interest that was both an outlier and identified in our genotype-phenotype association. The gene GA1 codes for gibberellic acid that is involved in internode elongation and height and corroborates the observed trait variation. These results combining phenotypic reciprocal gardens and genetic studies provide insight into plasticity of adaptive traits and genetic divergence and may help inform sourcing for grassland restoration in future drier climates.