Plant ranges are often made up of core areas where the distribution is continuous and the population density is high with small disjunct populations at the margins of the core. One well-studied type of disjunct population is formed by long distance dispersal as plants migrate away from disjunct Pleistocene refugial populations. The retreat of the Wisconsinan glaciation resulted in the outward dispersal of many plant species from their refugial locations to areas with suitable habitat. Many plants expanded their ranges through rare-long-distance dispersal.
This study used microsatellites to compare the genetic diversity, inbreeding levels, and gene flow frequency of disjunct Magnolia tripetala populations to main core M. tripetala populations. In addition, I determined that distance of dispersal is related to genetic diversity and identified source populations for the main core and northern disjunct populations.
There was no significant difference between the genetic diversity of disjunct populations and their counterparts. Inbreeding levels were high and gene flow was low among populations. Long-distance dispersal was determined to have a negative correlation with genetic diversity. Gene flow was traced from the refugial populations through the main core and into the northern disjunct populations. Magnolia tripetala has a range made up of fragmented populations through the core with further disjunct populations at the border of the core. M. tripetala was determined to have abundant genetic diversity and disjunct populations are not in immediate danger of genetic deterioration.
When conducting a study on disjunct populations, species should be compared based on phylogenetic relationships. Furthermore, disjunct populations should not be generalized as having low genetic diversity. Instead, factors such as species traits and population history of a species should be taken into account in order for a more accurate hypothesis to be made.
Advisor(s) or Committee Chair
Dr. Jarrett Johnson, Dr. Albert Meier
Gilkison, Victoria A., "Comparisons of Genetic Diversity Among Disjunct Populations of Magnolia tripetala" (2013). Honors College Capstone Experience/Thesis Projects. Paper 423.