Population history provides foundational knowledge for utilizing and developing native plant restoration materials

Authors: MASSATTI, ROB - Us Geological Survey (USGS); PRENDEVILLE, HOLLY - Us Forest Service (FS); Larson, Steven; RICHARDSON, BRYCE - Us Forest Service (FS); Waldron, Blair; KILKENNY, FRANCIS - Us Forest Service (FS)

Submitted to: Evolutionary Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2018
Publication Date: 9/1/2018
Citation: Massatti, R., Prendeville, H.R., Larson, S.R., Richardson, B.A., Waldron, B.L., Kilkenny, F. 2018. Population history provides foundational knowledge for utilizing and developing native plant restoration materials. Evolutionary Applications. 11(10):2025-2039. https://doi.org/10.1111/eva.12704.
DOI: https://doi.org/10.1111/eva.12704

Interpretive Summary: Populations can be defined as discernable groups of organisms, of the same species, that interbreed and have some relevant geographic distribution and history. Although populations tend to accumulate genetic differences over time, it is often difficult to discern how populations are truly structured in nature. Thus, population structure is often not incorporated into the development and use of native plant restoration materials, even though it is relevant factor. Bluebunch wheatgrass is a critical part of grassland and shrubland plant communities across the western United States, and it is commonly used for rangeland revegetation in this region. We used DNA sequencing data from 1155 unique plants, collected from 215 natural sites, to investigate genetic differences, geographic distributions, and the natural history of bluebunch wheatgrass populations. Genetic diversity of this species was partitioned into populations that likely differentiated since the Last Glacial Maximum. There is ongoing gene flow between adjacent populations, though estimated rates of migration vary from multiple migrants per generation to multiple generations per migrant. Cultivated germplasm sources remain genetically representative of the wildland localities from which material was originally collected, and they have high levels of genetic diversity. However, the cultivated germplasm sources represent a small fraction of the overall species diversity. Given the low migration rates and long divergence times between eastern and western populations, using cultivated germplasm sources from eastern populations may cause outbreeding depression in western locations. Characterizing the genetic diversity geographic distribution, and history of populations can guide the development and deployment of plant materials, with the goal of supporting species and community resilience and improving restoration outcomes.

Technical Abstract: Genetic structure and variation are often not incorporated into the development and use of native plant restoration materials even though genetic diversity is recognized as an important component of healthy ecosystem functioning and a factor that may influence restoration outcomes. In the western United States, Pseudoroegneria spicata (bluebunch wheatgrass, Poaceae) is an important component of grassland and shrubland plant communities and commonly used for ecological restoration due to its drought resistance and ability to compete with exotic weeds. We used next-generation sequencing data to investigate the processes that shaped P. spicata's geographic pattern of genetic variation across the Intermountain West. Pseudoroegneria spicata'a genetic diversity is partitioned into populations that likely differentiated since the Last Glacial Maximum. There is ongoing gene flow between adjacent populations, though migration rates vary from multiple migrants per generation to multiple generations per migrant. Regarding the native plant materials used in restoration, propagated germplasm sources remain genetically representative of the wildland localities from which material was originally sourced, and they have high levels of heterozygosity and nucleotide diversity. However, the propagated germplasm sources represent a small fraction of the overall genetic diversity of P. spicata. Given the low migration rates and long divergence times between eastern and western P. spicata populations, using propagated germplasm sources in eastern populations may facilitate outbreeding depression. A portion of the wildland P. spicata sampling localities in our study are now maintained by the National Genetic Resources Program, and we found that they often harbored lower genetic diversity and significant admixture. These results illustrate the importance of using proper guidelines to collect and maintain the integrity of germplasm, especially for outcrossing species. Characterizing the genetic diversity, geographic distribution, and history of populations can guide the development and deployment of plant materials, with the goal of supporting species and community resilience and improving restoration outcomes.