Date of Award:
Doctor of Philosophy (PhD)
Karen E Mock
Despite a thorough understanding of the proximate mechanisms that drive genetic diversity, we are still very poor at predicting the genetic diversity of natural populations. Understanding patterns of genetic diversity is important for many reasons, including predicting species' adaptation to climate change and predicting the spread of invasive species, but it is particularly important for species that are declining. This dissertation attempts to explain patterns in genetic diversity at multiple spatial scales across the range of the Northern Leopard Frog, Rana pipiens, which is declining across large portions of its range. Genetic diversity is often lower in edge populations than in central populations. Genetic diversity may be reduced in edge populations per se, or populations that occur at the edge of the species' range may have low diversity because they have recently expanded into new habitat and thus show signs of founder effects. In Chapter 2, we tested several alternative hypotheses to explain genetic diversity across the species' range, and to explain why some edge populations may not show reduced genetic diversity. We found that genetic diversity was reduced in edge populations relative to central populations, but was not reduced in populations in previously glaciated areas relative to previously unglaciated areas; therefore position at range edge had a stronger effect in reducing diversity than recent colonization of new habitat. We found that genetic diversity declined linearly towards the range edge in one of two transects from range center to range edge. We concluded that genetic diversity in this species is generally reduced by position at the range edge, but that this effect may differ among edges. In Chapter 3, we tested the hypothesis that eastern and western populations were genetically distinct. We found two distinct clades that introgress in some markers but are distinct and defined by narrow boundaries in the eastern Great Lakes region in others. We concluded that genetic diversity in the Mississippi River region was elevated by the introgression of descendants from two Pleistocene refugia. In Chapter 4, we analyzed genetic diversity within populations throughout Arizona to assess potential source populations for reintroductions. We also analyzed mitochondrial DNA to determine whether any populations contained genetic material not native to the region. Populations in one area had high genetic diversity and high gene flow among populations, but also contained evidence of introduction of eastern frogs. We conclude that supplementing genetic diversity in other populations with translocations from this area is not recommended.
O'Donnell, Ryan P., "Genetic diversity and genetic structuring at multiple spatial scales across the range of the Northern Leopard Frog, Rana pipiens" (2012). All Graduate Theses and Dissertations. 1296.
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