[PCA] New research supports restoration across the western US

Fri May 29 14:16:16 CDT 2020

Hi everyone,

Three papers recently published out of the USGS Southwest Biological Science Center (SBSC) discuss how genetics can inform restoration across the Intermountain West. Two papers document genetic patterns in James’ galleta grass (Hilaria jamesii, aka Pleuraphis jamesii), an important dryland bunchgrass species across the southwest. The authors first investigated<https://onlinelibrary.wiley.com/doi/pdf/10.1111/ecog.04840> landscape-level patterns of genetic variation and historical factors (e.g., post-glacial warming) influencing contemporary patterns of adaptation in James’ galleta grass. These data underlie recently-released<https://www.blm.gov/sites/blm.gov/files/GWRC_STZ_report1.pdf> genetically-based seed transfer zones (STZs) that account for both neutral and adaptive patterns of genetic variation. In the second paper<https://onlinelibrary.wiley.com/doi/10.1111/rec.13189>, the authors discuss evidence of hybridization where James’ galleta grass comes into contact with its sister species, tobosa grass (Hilaria mutica). Importantly, the only available restoration material for James’ galleta grass, ‘Viva,’ is a hybrid between these two species. The third paper<https://onlinelibrary.wiley.com/doi/10.1111/rec.13142> discusses the application of provisional STZs not only to seed transfer but also native plant materials development for species where no other data are available. In short, due to the region’s complex topography and interactions with climatic changes during the Pleistocene, species’ patterns of genetic variation are highly variable. As a result, STZs, even when constrained by ecoregions, are large enough that they may facilitate the mixing of highly genetically differentiated individuals, which can lead to unexpected and potentially negative outcomes after restoration efforts. Suggestions to mitigate risks are provided by assessing available genetic data for other plant species distributed across this region.

This research was funded by the BLM’s Colorado Plateau Native Plant Program and carried out by SBSC’s Genetics for Western Restoration and Conservation (GWRC)<https://www.usgs.gov/centers/sbsc/science/genetics-western-restoration-and-conservation-gwrc?qt-science_center_objects=0#qt-science_center_objects> group (www.usgs.gov/sbsc/gwrc<https://www.usgs.gov/centers/sbsc/science/genetics-western-restoration-and-conservation-gwrc?qt-science_center_objects=0#qt-science_center_objects>). The GWRC group designs and implements a range of genetic investigations to support conservation and restoration. To date, the GWRC group has explored patterns of genetic variability, demographic and evolutionary processes, and human impacts across a variety of priority restoration species, species of conservation concern, and invasives throughout the Intermountain West and beyond. You can find updates regarding GWRC group research by following SBSC on our Twitter account (@USGSAZ) or contacting USGS scientist Rob Massatti (rmassatti at usgs.gov<mailto:rmassatti at usgs.gov>).

 PAPER ABSTRACTS:

Paper 1:

The historical context of contemporary climatic adaptation: a case study in the climatically dynamic and environmentally complex southwestern United States

R Massatti & LL Knowles

Abstract: The process of adaptation can be highly dependent upon historical and contemporary factors, especially in environmentally and topographically complex regions affected by Pleistocene glaciations. Here, we investigate Hilaria jamesii (Poaceae), a dryland C4 graminoid, to test how patterns of adaptive genetic variation are linked to its glacial and post‐glacial history. We show that the species persisted in a single, southern refugium during the last glacial period and subsequently migrated throughout its current distribution concurrent with post‐glacial warming. The species’ putative adaptive genetic variation correlates with climatic gradients (e.g. monsoon precipitation and mean diurnal temperature range) that covary with the species’ probable route of demographic expansion. The short timescale and multiple climatic dimensions of adaptation imply that natural selection acted primarily upon standing genetic variation. These findings suggest that restoration and conservation practices should prioritize the maintenance of standing genetic variation to ensure that species have the capacity to respond to future environmental changes.

Paper 2:

Unexpected hybridization reveals the utility of genetics in native plant restoration

DE Winkler & R Massatti

Abstract: Native plant materials (NPMs) are increasingly utilized during the restoration of disturbed plant communities. Here, we analyze next‐generation genetic sequencing data for Hilaria jamesii, a dominant graminoid across drylands of the southwestern United States, and document that the species' only commercially‐available NPM, ‘Viva’, is a hybrid between H. jamesii and its sister species, H. mutica. In fact, hybrids between these species are common where they geographically overlap. Furthermore, we show that the ‘Viva’ hybrid has successfully been moved beyond the hybrid zone and into the core range of H. jamesii. The potential ramifications of introducing novel genetic material into H. jamesii are discussed, as well as the utility of genetic analyses to protect species natural patterns of genetic diversity and help managers make informed decisions regarding the development and deployment of NPMs.

Paper 3:

Assessment of population genetics and climatic variability can refine climate-informed seed transfer guidelines

R Massatti, RK Shriver, DE Winkler, BA Richardson & JB Bradford

Abstract: Restoration guidelines increasingly recognize the importance of genetic attributes in translocating native plant materials (NPMs). However, when species‐specific genetic information is unavailable, seed transfer guidelines use climate‐informed seed transfer zones (CSTZs) as an approximation. While CSTZs may improve how NPMs are developed and/or matched to restoration sites, they overlook genetic factors that can diminish restoration success and/or deteriorate natural patterns of genetic diversity and environmental factors that may introduce unexpected variation. Here, we analyze molecular data and geographic patterns of environmental variability across the western United States and demonstrate how they can refine CSTZs. Using genetic data available for 13 relevant plant species, we found that the probability of mixing genetically differentiated individuals (i.e. from different evolutionary lineages, or populations) was approximately 8% when considering locations separated by 50 km and reached nearly 80% by 500 km, which are distances relevant to ecoregionally constrained CSTZs. Furthermore, climate analyses revealed that geographically proximate locations are likely to maintain environmental similarity, regardless of CSTZ or ecoregion assignment. These results suggest constraining CSTZ‐informed seed transfer decisions by distance may mitigate the opportunity for negative genetic outcomes. Furthermore, environmental variability and/or specificity of NPMs (depending upon the restoration strategy) should be achieved by sourcing NPMs from geographically proximate locations to avoid introducing excessive genetic differentiation. Our results highlight the utility of combining molecular genetic data with other genetic inferences (i.e. of adaptation) to determine how best to transfer seed across restoration species' ranges and develop new restoration materials.

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Todd Wojtowicz

Science Communication

Southwest Biological Science Center

U.S. Geological Survey

Website: https://www.usgs.gov/centers/sbsc

Twitter: @USGSAZ

Office Phone: (928) 556-7390

Cell Phone: (928) 856-0076

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