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Biologists have long been interested in the diversity of organisms on earth. With their joint presentation to the Linnean Society of London in 1858, Darwin and Wallace proposed natural selection as a clear mechanism to explain the diversity of life. In the 155 years since this seminal presentation, evolutionary biologists have explored the patterns and processes of diversification in a vast number of taxonomic groups, including proposing additional mechanisms and confirming the dominant presence of natural selection in the role of diversification. The last few decades have seen rigorous debates on the study of these patterns and processes (e.g. adaptive radiation, species concepts) and advances in theory, data acquisition, and analytical methods to address a number of questions associated with diversification. Yet, much of the attention has been on model systems, resulting in deficiencies in our knowledge of how widespread certain phenomena are (e.g. adaptive radiation) or how general certain modes of speciation may be. In the present study, I explore various patterns and processes responsible for the diversification of salamanders in the Spelerpinae (Caudata: Plethodontidae). I examine the role of adaptive radiation in the subfamily, using a completely sampled phylogeny based on multiple loci, by testing a number of predictions based on general theory of the process. I also test a number of hypotheses to explain the diversification patterns observed in a range-wide phylogeographic analysis of the Eurycea quadridigitata species complex. Finally, I use a multilocus nuclear phylogeny and a relatively new species delimitation method to test whether genetic lineages are linked to breeding habitats represent distinct species. Using the species delimitation results, I look for congruence in a number of morphologic traits. I find that adaptive radiation is not a good model for the diversification of the Spelerpinae. In addition, I show strong molecular evidence that habitat isolation has likely lead to ecological speciation in at least three lineages of the complex, with moderate support from the morphology.
A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Scott J. Steppan, Professor Directing Dissertation; William C. Parker, University Representative; Joseph Travis, Committee Member; Austin R. Mast, Committee Member; Peter Beerli, Committee Member; D. Bruce Means, Committee Member.
Florida State University
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