ANALYSIS OF NATIVE AND INTRODUCED POPULATIONS OF AN INVASIVE PLANT: MANAGEMENT OF MEDUSAHEAD (TAENIATHERUM CAPUT-MEDUSAE) IN WESTERN US

Medusahead (Taeniatherum caput-medusae) is an annual grass that has invaded large areas of western United States. The distribution and abundance of this species increased greatly since the 1930s, and it now occupies millions of acres of the intermountain west. Genetic markers have previously been used to determine the distribution of genotypes in 45 populations from California, Idaho, Nevada, Oregon, Utah and Washington. These data are consistent with the pattern associated with multiple introduction events, and such introductions are believed to contribute to the severity of invasion. In this project, I will analyze both native and introduced populations of medusahead to determine the factors that have contributed to the invasion of this grass in the western U.S. Fifty to 55 native populations will be analyzed using these same genetic markers to determine whether a multiple introduction hypothesis is supported, and to identify source populations or regions in the native range of the species. Additionally, I will determine how variation for ecologically important traits is partitioned within and among native and introduced populations by conducting a greenhouse study. Results from this phase of the study will allow me to determine whether the invasion of medusahead in the western U.S. occurred through he introduction of genotypes pre-adapted to the western U.S., or through evolution following introduction, or both. Findings from this study will prove useful in the design and execution of efforts to develop biological control agents for medusahead. Thus, this research will provide valuable information for the management and control of medusahead.