Fine-scale spatial genetic structure in a locally abundant native bunchgrass (Achnatherum thurberianum) including distinct lineages revealed within seed transfer zones

Abstract

Analyses of the factors shaping spatial genetic structure in widespread plant species are important for understanding evolutionary history and local adaptation and have applied significance for guiding conservation and restoration decisions. Thurber needlegrass (Achnatherum thurberianum) is a widespread, locally abundant grass that inhabits heterogeneous arid environments of western North America and is of restoration significance. It is a common component of shrubland steppe communities in the Great Basin Desert, where drought, fire, and invasive grasses have degraded natural communities. Using a reduced representation sequencing approach, we generated SNP data at 5,677 loci across 246 individuals from 17 A. thurberianum populations spanning five previously delineated seed zones from the western Great Basin. Analyses revealed pronounced population genetic structure, with individuals forming consistent geographical clusters across a variety of population genetic analyses and spatial scales. Low levels of genetic diversity within populations, as well as high population estimates of linkage disequilibrium and inbreeding, were consistent with self-fertilization as a contributor to population differentiation. Moreover, variance partitioning and partial RDA indicated local adaptation to the environment as an additional factor influencing the spatial distribution of genetic variation. The environmental variables driving these results were similar to those implicated in recent genecological work which inferred local adaptation in order to delineate seed zones. However, our analyses also reveal a complex evolutionary history of A. thurberanium in the Great Basin, where previously delineated seed zones contain distantly related populations. Overall, our results indicate that numerous factors shape genetic variation in A. thurberianum and that evolutionary history, along with differentiation across distinct geographic and environmental scales, should be considered for conservation and restoration plans.

Does a history of population co‐occurrence predict plant performance, community productivity, or invasion resistance?

“…Sites were primarily mid-elevation, sagebrush steppe communities, with average annual precipitation between 237 and 384 mm and elevation ranging from 1395 to 2055 m (Appendix S1: Table S1; PRISM Climate Group, 2004). While it is not possible to know the duration of occupancy for each species in each site, or the degree of gene flow among populations for each species, genetic analyses for several species from these sites (Faske et al, 2021;Osuna-Mascar o et al, 2023) suggest moderate to strong isolation, and the opportunity for independent evolution, for even the most proximate populations (e.g., Peavine and Patagonia; Figure 1). We bulk-collected mature seeds for each species in each location from a minimum of 50 individual plants, with a minimum of 1 m separating individuals, between 1 June and 15 December of 2015.…”