GRADUATE PROGRAM IN PLANT BIOLOGY PH.D. DISSERTATION DEFENSE SEMINAR
will present a seminar entitled
“Evolutionary and Demographic Processes in the Invasive Weed Microstegium vimineum”
Tuesday, February 14, 2012
9:00a.m. – 10:00 a.m.
Alampi Room, IMCS
Marine & Costal Sciences Building
ADVISOR: Jean Marie Hartman
Jean Marie Hartman
Microstegium vimineum (Trin.) A. Camus (Japanese stiltgrass; Poaceae) is considered among the most invasive plants in the eastern United States. There has been considerable study of this species’ ecology and management though far less attention has been paid to its molecular ecology and the evolutionary processes which may influence its invasion success. Here, I describe a newly developed molecular marker system (microsatellite) which I used to examine M. vimineum’s genetic population structure and diversity in both its native and introduced ranges. I found clear signals that M. vimineum’s mating system is the most important determinant of the species’ population structure and variability. The invasive range had lower genetic diversity overall, probably due to founder effects. Also, as is often observed in invasive organisms, population and regional genetic differentiation appeared to be ‘in process’ in the invasive range. Genetic divergence and differentiation in the invasive range are likely to continue as the species expands its range. Furthermore, M. vimineum’s mixed cleistogamous/chasmogamous mating system allows for the near fixation of microsatellite genotypes in a given population by high rates of selfing, while still permitting the persistence of allelic diversity and generation of new genotypes at low frequency via occasional outcrossing. Thus, this mating system may confer adaptive advantage to the species as it settles upon ‘fit’ genotypes in a given area while retaining evolutionary potential for range expansion into new habitats. I also attempted to discern adaptively significant phenotypes in M. vimineum through the measurement of phenological variation of plants originating from across the species’ invasive range under manipulated light treatments. Flowering time and biomass were both strongly correlated with the latitude of population origin such that populations collected from more northern latitudes flowered significantly earlier at lower biomass than populations from southern locations. This pattern suggests rapid adaptive evolution of phenology over a period of less than one hundred years, and such changes have likely promoted the northward range expansion of this species. Interestingly, barriers to gene flow, including bottlenecks and inbreeding, have apparently not forestalled adaptive processes for this plant. Based on literature review and this new data, I hypothesize that adaptive evolution of phenology may be widespread in many invasive plant species and an essential process during range expansion.