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Genetic variation and local adaptation at a cheatgrass (Bromus tectorum) invasion edge in western Nevada

Authors

  • ELIZABETH A. LEGER,

    1. Department of Natural Resources and Environmental Science, University of Nevada, Reno, 1664 N. Virginia Street, MS 370, Reno, NV 89557, USA
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  • ERIN K. ESPELAND,

    1. Department of Natural Resources and Environmental Science, University of Nevada, Reno, 1664 N. Virginia Street, MS 370, Reno, NV 89557, USA
    2. USDA ARS NPARL, 1500 N. Central Ave., Sidney, MT 59270, USA
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  • KEITH R. MERRILL,

    1. Department of Plant and Wildlife Science, Brigham Young University, Provo, UT 84601, USA
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  • SUSAN E. MEYER

    1. US Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo, UT 84606, USA
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  • E. Leger's research focuses on applied evolutionary questions in the Great basin. E. Espeland studies environmental stress, plant–plant interactions, and their effects on evolutionary processes. K. Merrill conducted the SSR genotyping while an under graduate at Brigham Young University, and is now a Master's student with S. Meyer. S. Meyer's current research is focused on the evolutionary ecology of Bromus tectorum and its coevolutionary relationships with fungal pathogens.

Elizabeth Leger, Fax: (775) 784 4789; E-mail: eleger@cabnr.unr.edu

Abstract

Cheatgrass (Bromus tectorum) is an invasive weed in western North America found primarily growing at elevations less than 2200 m. We asked whether cheatgrass is capable of becoming adapted to a marginal habitat, by investigating a population at a high elevation invasion edge. We used a combination of methods, including reciprocal field transplants, controlled environment studies and molecular analysis. High levels of SSR gene diversity (0.50 vs. 0.43) and comparable variation in phenotypic traits were observed at both the invasion edge and a low elevation, high-density population. Three heterozygotes were observed in the edge population, which is unusual in this predominantly self-pollinating plant. Plants from high elevations germinated more slowly in a growth chamber and had slower seedling growth rates. Survivorship was low at the edge (13%), compared with the low elevation site (55%), but surviving plants were of similar size and had equivalent reproductive output. Seed size positively affected survival and plant performance in the field and this trait was inherited. Emergence timing affected survival at the low elevation site and germination timing was also inherited. Local adaptation was seen in the low, rather than in the high elevation site, because of differential survival. While there was no evidence for local adaptation to the high elevation site observed in the field, family level and genotype-level differences in traits that affected field performance, high genetic diversity at the invasion edge, and evidence of outcrossing in this highly selfing species indicates that the potential for adaptation to a marginal habitat exists within this population.

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