Submitted to: Agricultural Research Service Publication
Publication Type: Abstract Only
Publication Acceptance Date: 10/28/2004
Publication Date: 11/4/2004
Citation: Larson, S.R., Jones, T.A., Jensen, K.B. 2004. Phylogeography of bluebunch wheatgrass. Agricultural Research Service Publication.
Technical Abstract: Bluebunch wheatgrass (Pseudoroegneria spicata) is an abundant, allogamous species widely adapted to the temperate, semiarid steppe and open woodland regions of western North America. Highly palatable to livestock and amenable to cultivated seed production, this species has been widely used for rangeland revegetation. Amplified DNA fragment length polymorphism (AFLP) was used to investigate genetic diversity and population structure among 565 P. spicata plants grown from 82 seed collection sites (localities) representing much of the species distribution. Bluebunch wheatgrass plants group almost strictly by locality and geographic region based on neighbor-joining cluster analysis of Euclidean distances (the number of DNA polymorphisms) and similarity coefficients (proportion of shared DNA fragments) among individual genotypes. Significant apportionment of DNA polymorphism among accessions (32%) was detected by analysis of molecular variance (AMOVA), indicating restricted gene flow among seed collection site demes. The average total number of DNA polymorphisms among localities was signifciantly correlated (r>0.58) with geographical distance. The optimum Bayesian clustering model included 21 genetic groups, indicating restricted gene flow and dispersal among hierarchical groups of demes. Significant differentiation among these 21 metapopulations was also supported by AMOVA and other nonparametric methods of hypothesis testing based on DNA similarity coefficients. Moreover, the average total number of DNA polymorphisms among Bayesian groups was significantly correlated (r=0.53) with the average geographic distance among corresponding seed collection sites. Approximately 18.3% of the DNA polymorphism was partitioned among the 21 regional groups, 14.9% among localities within groups, and 66.8% within accessions. Thus, gene flow and dispersal among bluebunch wheatgrass collection sites was restricted among demes and larger regional metapopulations. Although collection site demes may be subject to multiple extinctions and recolonizations, metapopulations are expected to persist far longer than component demes. Although plant demes are the more obvious and recognizable form of population structure, geographically significant metapopulations may be more relevant units for research and development of plant materials used for rangeland revegetation.