Multi-Scale Population Genetic Analysis of Cogongrass (Imperata Cylindrica) in the Southeastern United States: Introduction History, Range Expansion, and Hybridization

Biological invasions are a significant area of research due to perceived negative environmental and economic impacts. The study of biological invasions has identified three broad components involved in successful invasions: propagule pressure, abiotic and biotic conditions. Propagule pressure is the product of introduced propagules and the frequency of those introductions, and is considered a driver in all stages of invasion. Data to quantify propagule pressure is often unavailable, and therefore, this research approached genetic information to produce estimates of propagule pressure in the successful invasion of cogongrass (Imperata cylindrica) in the United States. The following research utilized molecular methodologies to estimate genetic diversity and to infer historical introductions. Population genetic analyses were conducted for the purpose of estimating extant population-level genetic diversity at multiple-scales to first address documented cogongrass introduction(s) into this country, followed by an exploration of substantial range expansion into seven states across the region. Lastly, this research explicitly seeks evidence to support interspecific hybridization between cogongrass and a co-occurring congeneric (Imperata brasiliensis) having occurred. Aggressive range expansion by cogongrass has been attributed to such a hybridization event, but has not yet been specifically tested. Historical accounts of foreign introduction of cogongrass propagules identify two separate introductions of distinct source material made into Mississippi and Alabama. Localized population genetic analysis of these two states found substantial genetic variability within and among cogongrass populations, and supported a two-introduction scenario of distinct genetic source propagules establishing and subsequently intermixing. Enlarging the geographic scale of study incorporated five additional U.S. states currently experiencing and managing cogongrass invasion. Considerable genetic variability was found within and among the seven states surveyed. It was found that range expansion was unequal across the range, and that the most distant states tested were not genetically isolated from source populations, suggesting a possible anthropogenic role. Focusing solely on Florida where two congeners overlap ranges, morphology, and ecology, this population genetic analysis failed to detect significant evidence to support interspecific hybridization. Collectively, these investigations explored genome-level dynamics during invasion by a noteworthy invasive grass in an effort to better understand the process of biological invasions