Snoke, Margaret  (University of Georgia).  Mentor:  Eric Nagy (University of Virginia).  Molecular and Morphological study of Hybridization in Monarda fistulosa
and M. clinopodia.

Abstract: Hybridization plays an interesting and important role in evolution because it creates new genotypes, allows geneflow, and may lead to speciation. Specifically, introgressive hybridization allows gene flow betweem hybridizing species and the incorporation of genes from one species into another. Introgression can lead to speciation, increase genetic variation, and increase or decrease fitness, depending on the traits passed betweem species. This study looks at hybridization between two species of Monarda (Lamiaceae). The study reports on preliminary molecular work done to differentiate the two species as well as morphological measurements taken to explore variation among Monarda populations and within a hybrid population of M. fistulosa and M. clinapodia. Standard molecular DNA extraction and PCR techniques were used to identify probably cpDNA markers that differentiate the two species. Morphological measurements of three characteristics with a strong genetic component were taken at 17 individual sites of Monarda to try and identify populations that seemed to be consistent with characteristics of M .fistulosa and M. clinapodia, as well as look for intermediate sites that might be hybrid populations. The results indicated that of the 17 sites samples, thre were sites that fell into each of the three catagories. In addition, a hybrid site between M. fistulosa and M. clinopodia was sampled more in depth to explore the dynamics of hybridization between these two species and what this might indicate about gene flow in the hybrid zone. The hybrid site was an old field community surrounded by native woodland. Transects were laid 5m, 10m, and 20m from the border of where the field met the woods. Individuals were sampled along eac of these transects, including the border.  Results indicated that the shape of the hybrid cline had a steep slope downward from 20m in the woods to the border and then leveled off across the field. This type of cline seems indicative of unidirectional gene flow. Possibly explainations for unidirectional gene flow include reproductive barriers, selection, or density differences between the two species.