Strong patterns of intraspecific variation and local adaptation in Great Basin plants revealed through a review of 75 years of experiments

Authors: BAUGHMAN, OWEN - University Of Nevada; AGNERAY, ALISON - University Of Nevada; FORISTER, MATTHEW - University Of Nevada; KILKENNY, FRANCIS - Forest Service (FS); Espeland, Erin; FIEGENER, ROB - Applied Ecological Services, Inc; HORNING, MATT - Us Forest Service (FS); Johnson, Richard; KAYE, THOMAS - Applied Ecological Services, Inc; OTT, JEFFREY - Forest Service (FS); ST. CLAIR, J - Forest Service (FS); LEGER, ELIZABETH - University Of Nevada

Submitted to: Royal Society Open Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2019
Publication Date: 4/26/2019
Citation: Baughman, O.W., Agneray, A.C., Forister, M.L., Kilkenny, F.F., Espeland, E.K., Fiegener, R., Horning, M.E., Johnson, R.C., Kaye, T.N., Ott, J.E., St. Clair, J.B., Leger, E.A. 2019. Strong patterns of intraspecific variation and local adaptation in Great Basin plants revealed through a review of 75 years of experiments. Royal Society Open Science. 9:6259–6275. https://doi.org/10.1002/ece3.5200.
DOI: https://doi.org/10.1002/ece3.5200

Interpretive Summary: Local adaptation is a widespread phenomenon in plants. Over and over, we find that plants exhibit higher fitness (survival, reproductive output, or biomass accumulation) in their home environment compared to when they are transplanted to distant locations. When local adaptation occurs, we expect to see signatures of 1) differences among populations, 2) correlations between among-population differences and the environments of the source populations, and 3) higher fitness of local over nonlocal populations. We asked how frequently each of these three signatures have been observed among populations of plant species native to North America’s Great Basin, including which (if any) traits show associations with mean annual precipitation (MAP) and mean annual temperature (MAT). We used 170 published studies that compared multiple populations in one or more common environments. Of the experiments applicable to each signature, we found 95.1% of 305 experiments reported differences among populations (signature 1), 81.4% of 161 experiments found relationships between populations and their environment (signature 2), and 69% of 27 experiments reported greater local performance (signature 3): 90% of studies that measured reproductive output showed greater local fitness. Biomass was not a good indicator for fitness, compared to reproductive output and survival measures. This result indicates that plant varieties or cultivars improved and bred for vigor may not do well in this landscape. We found strong relationships between differences in flowering time and differences in MAT. We also found associations between leaf size and MAT, and survival, shoot mass, inflorescence number, and flowering time with MAP. Our results demonstrate widespread climate-related population differentiation and local adaptation in the Great Basin. We conclude that plants in the Great Basin are likely to be adapted to climate, which varies throughout the region. Using locally-sourced seeds will therefore increase restoration success in this region, which contrasts the widespread restoration practice of large scale application of commercially-available seed whose origins lie outside the Great Basin.

Technical Abstract: When organisms experience variation in the magnitude and direction of natural selection across the landscape, we expect to see 1) differences among populations in phenotypic traits, 2) correlations between these traits and habitat-related variables, and 3) higher fitness of local over nonlocal populations in reciprocal transplantation. We asked how frequently each of these three signatures have been observed among populations of plant species native to North America’s Great Basin, including which (if any) traits show associations across taxa with mean annual precipitation (MAP) and mean annual temperature (MAT). We conducted a broad literature search, locating 170 published studies that compared phenotypic traits of multiple populations in one or more common environments, representing 327 different experiments using over 2950 unique populations of 121 taxa of forbs, grasses, shrubs and deciduous trees. We documented the presence of each signature, and recorded which traits were involved. We also extracted population origin locations and published data on eight common phenotypic traits to look for cross-taxa patterns in the relationships between trait values and climates of origin (MAP and MAT) using pairwise differences among populations. Of the experiments suitable for each signature, we found 95.1% of 305 experiments reported differences among populations for at least one trait, 81.4% of 161 experiments reported trait/environment relationships, and 69% of 27 experiments reported greater local performance in at least one garden during at least one sampling date, with 90% of studies that measured reproductive output showing greater local fitness. Variation in all eight phenotypic traits was associated with both MAP and MAT, with notably strong relationships between differences in flowering time and differences in MAT, with additional associations between leaf size and MAT, and survival, shoot mass, inflorescence number, and flowering time with MAP. Our results demonstrate widespread habitat-related population differentiation and local adaptation in the Great Basin, where few locally-sourced populations of commonly-seeded native species are available for restoration. We conclude that locally-sourced seeds are likely to harbor adaptations that are relevant to restoration success in this region.