Genetic structure of Pseudoroegneria spicata in eastern Washington Palouse Prairie and Channeled Scablands

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Ethan T. Bean, Jessica L. Allen - PhD. and Rebecca L. Brown - PhD., Department of Biology, Eastern Washington University, Cheney, WA, Steve R. Larson - PhD., Forage & Range Research, USDA ARS, Logan, UT

Background/Question/Methods
Establishing genetically diverse communities that can adapt to dynamic selective pressures is a challenge that must be addressed in ecological restoration. However, the genetic structure of native plant species used for restoration is often poorly understood. The native bunchgrass, Pseudoroegneria spicata, is a keystone species of Inland Northwestern US ecoregions that has become a staple in commercially available restoration seed mixes. It was abundant in the endangered Palouse Prairie ecoregion, characterized by rolling hills of deep loess soil. Less than 1% of native Palouse Prairie is left, due to agricultural conversion, with remnants highly fragmented and isolated. P. spicata is also common in nearby Channeled Scabland habitats formed by glacial flooding and characterized by relatively shallow soils. Previous studies of the genetic structure of P. spicata have not included populations in these regions. Our goal was to assess the genetic structure of P. spicata across Palouse Prairie remnants and Channeled Scabland habitat in Eastern Washington, and determine how it relates to the genetic composition of commercially available seed. We hypothesized that habitat differences between the Palouse and Channeled Scablands could lead to genetic differentiation between P. spicata populations. We also expected that commercial plant material sourced from a smaller nearby site would be more closely related to plants from our sampling locations than plant material collected from a larger area and pooled. To test these hypotheses, plant DNA samples were collected from six locations in the Channeled Scablands and Palouse Prairie and two commercial sources. We calculated inbreeding coefficient, conducted principal component analyses, and used Bayesian cluster analysis in STRUCTURE to test for inbreeding, differentiation of populations, and relatedness of native propagule sources.
Results/Conclusions
We did not find signs of genetic differentiation in Pseudoroegneria spicata between sites on different soil types, rather genetic differentiation occurred along a north south latitudinal gradient. Commercially sourced seeds from the smaller collection area were more closely related to northern sites, while seeds sourced from the larger region were more similar to southern sites. There were no signs of inbreeding in commercial seed sources, however we found evidence of hybridization either between production fields or with local plant populations at a native seed nursery. Samples from Steptoe Butte State Park, one of the larger Palouse remnants, had a lower inbreeding coefficient than the rest of the sites, which highlights the importance of continued preservation of this prairie remnant.