Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Stephen Novak, Ph.D.


James F. Smith, Ph.D.


Rene Sforza, Ph.D.


Biological invasions are one of the main drivers of global change, and thus one of the main factors contributing to a loss of biodiversity world-wide. Introduced species can destroy habitat through predation, grazing, and competition for resources; spread disease; alter disturbance regimes; and disrupt ecosystem services. Taeniatherum caput-medusae subsp. asperum (medusahead) is a winter-annual grass native to Eurasia and invasive in the westernUnited States. Medusahead dominates one million hectares of its invasive range and detrimentally affects the areas it inhabits through degradation of foraging value for livestock, increasing fire frequencies, and decreasing biodiversity. Previously, allozyme analyses have suggested this highly selfing species exhibits low genetic diversity within populations and high differentiation among populations in the invasive range. In this study, I used a dominant, multilocus molecular marker, amplified fragment length polymorphisms (AFLPs), to assess the genetic diversity and structure of 52 invasive populations of medusahead, evaluate the influence of propagule pressure and founder events during establishment, identify putative source regions, and compare my AFLP results to past allozyme results. Using 110 AFLP loci, 15 multilocus genotypes (utilizing an error rate of 3 loci) were detected among invasive populations, and I estimated that the number of independent introductions ranged from eight to 11. These data suggest moderate propagule pressure for the introduction of medusahead into the western United States. Despite moderate propagule pressure, my data revealed that invasive populations had relatively low genetic diversity and high genetic structure, compared to plants with similar life-history traits (e.g., a highly selfing, gravity-dispersed, annual plant species). Moreover, the lower level of genetic diversity of invasive populations, compared with native populations, provides evidence that founder effects have influenced the diversity of invasive populations of medusahead. Putative source regions were narrowed to southernFrance and southeasternEurope. However, several lines of evidence clearly pinpoint seven populations from easternBulgaria, the Crimean peninsula,Russia, and centralGreece as the most likely source populations for this invasion. My findings are generally similar to that of previous allozyme studies; although my estimates of genetic diversity are higher than the estimates using allozymes. Results of this study point to the additional insights into the invasion process that can be gained by using a more polymorphic molecular marker.