Khan, Amy (Saint Olaf College). Mentor: Eric Nagy (University of Virginia). A measurement of fitness in the woodfern genus Dryopteris within a hybrid zone.

Abstract: Hybridization within plants is common, and leads to large evolutionary changes, reflected by the fact that 30-80% of all plant species may have derived from hybridization events (Floate et al . 1993). Within the new hybrid species there may be characteristics intermediate to the two parental species, and traits resembling one or the other parental species (Kentner and Mesler 2000). Hybrids between taxa of different chromosome number are often sterile, unless they have undergone a polyploid event, and allowing for regular pairing in meiosis (Briggs and Walters 1990). There is also the possibility of triploids forming within the diploid population and having a significant effect on the evolution of new hybrid individuals (Ramsey and Schemske 1998). The ploidy level within hybrids can be tested with Flow Cytometry which measures the DNA content of the cell. In this study we correlate fitness of an allopolyploid fern hybrid with a hybrid index score and potential for herbivory in an effort to predict the evolutionary importance of the hybrid “taxa.” In determining the individual's overall fitness, we measured performance measures, including frond length, frond number and reproductive traits. We did not see any significant difference between the Hybrid Index Score and the performance or reproductive measures. We did see a significant difference in species herbivory, concentrated in the Dryopteris intermedia zone. Our study suggests that the evolutionary potential for hybrids and parental species is the same.