Distribution of Genotypes Within and among Taeniatherum Caput-medusae (Poaceae) Populations from Eastern Washington: Assessment of an Invasion at a Local Scale

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Stephen Novak


Multiple introductions from many source populations can increase the chance of introducing preadapted genotypes, increases standing genetic variation and increases the likelihood of adaptive evolution; all of which might contribute to invasion. Taeniatherum caput-medusae is an annual, highly self-pollinating grass that is invasive in the western United States. Through previous genetic analysis, five multilocus genotypes (MLG) were detected in the relatively small geographic area of eastern Washington, which suggests that multiple introductions have occurred in this region. Fifty-seven populations of T. caput-medusae from eastern Washington were assessed at 23 loci using starch gel electrophoresis. Based on these data a sixth MLG, Rattlesnake Station, was detected in the study area. The Steptoe Butte genotype, which was first introduced in 1901, has the largest range of the six genotypes and is creating polymorphic populations where it comes into contact with other genotypes. Founder effects appear to have reduced genetic diversity within and among populations from eastern Washington in comparison to native populations. The results of this study contribute to our understanding of the invasion process at a local spatial scale by reconstructing the introduction and range expansion of T. caput-medusae in eastern Washington.

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