Population Genetics of Invasive Plant Species

Invasive plant species offer special opportunities to study population genetics as their populations are often very dynamic in terms of population size, colonization ability and genetic composition. My special interest is to determine how the breeding system of invasive species affects their ability to colonize new sites and to rapidly expand their population sizes.

Albizia julibrissin (mimosa; Mimosoideae) - Mimosa is an introduced, early-successional, weedy tree that has become widespread in the southeastern US. Dr. M. J. Godt and I are examining spatial and temporal variation in mimosa’s reproductive biology to elucidate the population genetic processes that contribute to its ability to invade new habitats, establish populations and disperse to new sites. Multilocus allozyme data are being combined with ecological and demographic data to address a series of questions: Are isolated trees predominantly selfed or outcrossed? Do the number and frequency of pollen donors differ between isolated trees and trees within established populations? How do small, growing populations acquire genetic diversity? What proportion of the new recruits in growing populations are progeny of the initial founder? Does the breeding structure of populations change as they grow or senesce? Does gene flow differ between isolated trees and established populations? Has this introduced species adapted to different climatic regimes? Several characteristics of mimosa allow detailed analyses if its reproductive biology including abundant annual seed production, early maturity, high allozyme polymorphism and singly sired fruits. The identification of isolated trees and paired trees in nearby populations coupled with seven years of stored seed collections from these sites permit unprecedented insights into the spatial and temporal dynamics of the breeding structure of populations of this invasive tree during colonization and population establishment. Common gardens are being used to determine the degree of geographic variation that has evolved.



Godt, M. J. W. and J. L. Hamrick. 1997. Estimation of mating system parameters of Albizia julibrissin (Fabaceae). Forest Genetics 4:217-221.
Irwin, A.J., J.L. Hamrick, M.J.W. Godt and P.E. Smouse.2003. A multiyear estimate of the effective pollen donor pool for Albizia julibrissin. Heredity 90:187-194
Lee, J. M. and J. L. Hamrick. 1983. The demographic characteristics of two natural populations of musk thistle (Carduus nutans L.). Journal of Ecology 71:923-936.
Smyth, C. A. and J. L. Hamrick. 1987. Realized gene flow via pollen in artificial populations of Carduus nutans. Evolution 41:613-619.