Megan E. Ladd

Date of Graduation

Spring 2008


Master of Science in Biology



Committee Chair

L. Michelle Bowe


hybridization, elm trees, Ulmus, invasive species, AFLPs, cryptic invasion.

Subject Categories



Non-native species invasions are of high ecological importance due to their ability to transform native ecosystems. One such species, Siberian elm, has been shown to have been invading native landscapes across the central and eastern United States since the late 1800s. The natives, American elm and slippery elm, have declined dramatically due to Dutch elm disease throughout the mid- to late 1900s, creating open niches for the escaping Siberian elm. This physical invasion is clear, yet what is less clear is whether Siberian elm is also invading genetically through hybridization with the two native species. The goal of this study was to determine whether Siberian elm was genetically invading native elm populations by means of hybridization. Amplified fragment length polymorphisms (AFLPs), a type of genetic fingerprinting, was used to show evidence of hybridization. Using, population allocation, phylogenetic analyses, and non-metric multidimensional scaling (MDS), a multivariate statistical ranking program several hybrids were identified among the three species. I found both F2, 2-way, and 3-way hybrids which may suggest that multigenerational hybridizations have occurred. These findings have significant impact on the way physical invasions of species are viewed due to their cryptic nature. These cryptic hybrids may be more widespread than previously thought, indicating the need for a more thorough exploration of the potential effects that hybrids have on natural systems.


© Megan E. Ladd

Campus Only