Local adaptation, genetic divergence, and experimental selection in a foundation grass across the US Great Plains’ climate gradient

Abstract

Many prior studies have uncovered evidence for local adaptation using reciprocal transplant experiments. However, these studies are rarely conducted for a long enough time to observe succession and competitive dynamics in a community context, limiting inferences for long‐lived species. Furthermore, the genetic basis of local adaptation and genetic associations with climate has rarely been identified. Here, we report on a long‐term (6‐year) experiment conducted under natural conditions focused on Andropogon gerardii, the dominant grass of the North American Great Plains tallgrass ecosystem. We focus on this foundation grass that comprises 80% of tallgrass prairie biomass and is widely used in 20,000 km2 of restoration. Specifically, we asked the following questions: (a) Whether ecotypes are locally adapted to regional climate in realistic ecological communities. (b) Does adaptive genetic variation underpin divergent phenotypes across the climate gradient? (c) Is there evidence of local adaptation if the plants are exposed to competition among ecotypes in mixed ecotype plots? Finally, (d) are local adaptation and genetic divergence related to climate? Reciprocal gardens were planted with 3 regional ecotypes (originating from dry, mesic, wet climate sources) of Andropogon gerardii across a precipitation gradient (500–1,200 mm/year) in the US Great Plains. We demonstrate local adaptation and differentiation of ecotypes in wet and dry environments. Surprisingly, the apparent generalist mesic ecotype performed comparably under all rainfall conditions. Ecotype performance was underpinned by differences in neutral diversity and candidate genes corroborating strong differences among ecotypes. Ecotype differentiation was related to climate, primarily rainfall. Without long‐term studies, wrong conclusions would have been reached based on the first two years. Further, restoring prairies with climate‐matched ecotypes is critical to future ecology, conservation, and sustainability under climate change.

Adaptive genetic potential and plasticity of trait variation in the foundation prairie grass Andropogon gerardii across the US Great Plains’ climate gradient: Implications for climate change and restoration

“…Interestingly, our results do not agree with recent studies showing local adaptation of vegetative cover of wet and dry ecotypes in seeded community plots over 5 years (Galliart et al., 2019) where ecotypes grew with other species, as they would in nature. In the community plots, ecotypes compete with themselves and other species for resources such as light, nutrients, and water.…”

“…In contrast, the single plants of this reciprocal garden experiment grew without competition and rarely showed signs of local adaptation. Apparently, only in a realistic community do we observe local adaptation expressed in these ecotypes, showing the importance of biotic interactions in driving local adaptation (Bischoff et al., 2006; Grassein, Lavorel, & Till‐Bottraud, 2014; Galliart et al., 2019), thus highlighting the need to put local adaptation in the context of the community.…”

“…Nearly all plants of all ecotypes survived transplantation to all sites, even into western KS. Note that these reciprocal gardens with single‐spaced plants of only A. gerardii are a separate research platform (described Caudle, Johnson, Baer, & Maricle, 2014; Kramer et al., 2018; Maricle, Caudle, Lindsey, Baer, & Johnson, 2017; Mendola, Baer, Johnson, & Maricle, 2015; Olsen, Caudle, Johnson, Baer, & Maricle, 2013; Varvel et al., 2018) from reciprocal gardens with A. gerardii ecotypes planted with other prairie species in a seeded community (Galliart et al., 2019; Johnson et al., 2015; Maricle et al., 2017; Wilson, Gibson, Baer, & Johnson, 2016).…”

Spatial, climate and ploidy factors drive genomic diversity and resilience in the widespread grass Themeda triandra

“…Most research on genetic diversity in grass species has been undertaken on those of agricultural importance (Buckler, Thornsberry, & Kresovich, 2001) such as wheat, corn, rice and sorghum, or those that are being developed for biofuels such as switchgrass ( Panicum— Casler, Stendal, Kapich, & Vogel, 2007; Harrison, Gornish, & Copeland, 2015) and sugarcane ( Miscanthus —Vermerris, 2008). While research on species such as switchgrass have provided valuable insights into natural patterns of genetic diversity, adaptation across gradients and the role ploidy plays between these lines of enquiry (Grabowski, Morris, Casler, & Borevitz, 2014; Lowry et al., 2014, 2019; Morris, Grabowski, & Borevitz, 2011;), detailed genomic knowledge is needed for other ecologically important grasses, similar to the emerging example of Andropogon gerardii (Galliart et al., 2019; Gray et al., 2014; Johnson et al., 2015).…”

The evolution of thermal performance in native and invasive populations of Mimulus guttatus

“…Another TPC parameter that may track local thermal regimes is thermal optimum. Transplant experiments indicate that local adaptation is ubiquitous across many plant taxa (Savolainen, Pyhäjärvi, & Knürr, 2007; Hereford, 2009; Galliart et al, 2019). Adaptation to local climatic conditions in the introduced range may result in niche shifts in invasive populations relative to native populations (Chapman, Scalone, Štefanić, & Bullock, 2017; Konowalik & Kolanowska, 2018).…”