DISSERTATION RESEARCH: Untangling the Cystopteris fragilis Complex: An Investigation of the Effects of Polyploidy on Diversification Rates

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Arguably the most dramatic mutation possible (whole-genome duplication, or polyploidy) results in an individual with double the chromosome number of its parents. Polyploidy is a common and ongoing phenomenon in plants, where many crops, for example, are polyploid. This project aims to examine the evolutionary potential and fate of polyploid lineages in ferns¬¬a plant group where nearly all species have experienced one or more episodes of polyploidy in their evolutionary past. The globally distributed fern genus Cystopteris encompasses a complex mix of diploid and polyploid species, making it ideal for investigating the effects of polyploidy on diversification rates. Using DNA sequence data from 200 Cystopteris individuals, each of known ploidy level, evolutionary relationships will be inferred, ancestral ploidy levels will be reconstructed, and speciation and extinction rates will be estimated through time. Despite its ubiquity and scientific importance, the long-term potential and evolutionary dynamics of polyploidy remain contentious--are polyploid lineages "dead-ends" that are prone to rapid extinction, or do they instead drive evolutionary novelty? This empirical study is well positioned to make a key contribution to understanding the evolutionary importance of polyploidy, with implications for evolutionary theory, biodiversity conservation, and crop improvement.