A Morphological and Phylogenetic Comparative approach to investigating Branching Architecture Evolution in Monocots A Dissertation

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The inflorescence is a specialized reproductive branch that dictates flower positions,necessary for effective pollination. Over evolutionary time, changes in branching patterns have led to the evolution of highly diverse inflorescence architecture. This dissertation investigates the developmental and evolutionary origin of inflorescence branching architecture in monocots focusing on umbels, a type of branching architecture where all flowers appear to arise from a single point. The first chapter identifies, by comparative developmental morphology and anatomy, that there are at least three convergent architectures that produce an umbellate phenotype. Of those, there are three cases of parallel evolution. This highlights the liability of achieving this unique inflorescence form. Given that umbellate structures have evolved via distinct mechanisms, the second chapter aims to test if umbellate inflorescences conferred an adaptive advantage in those lineages. To do so, data was collected on inflorescence structure in all major lineages of monocots, including fossils, totaling more than 2500 species. A statistical phylogenetic framework was utilized to infer ancestral states in the monocots and test if umbels are correlated with shifts in diversification, with respect to all other inflorescence morphologies. Our results show that lineages with umbels have higher rates of diversification indicating this reproductive structure played an unappreciated role in the diversification of monocots. The models in the aforementioned approach are based largely on models of nucleotide substitution for discrete states. The third chapter seeks to achieve a more realistic understanding of branching architecture evolution by incorporating morphospaces into comparative analyses. This was done by “rescoring” inflorescence states using a published inflorescence morphospace in conjunction with the threshold model, a more biologically realistic model. A series of simulations were performed using a new multivariate implementation of the threshold model and found that it is sufficiently accurate in ancestral state inference. Then, this model was used to test a 200-year-old conjecture on the origin of the monocot umbel found in the Amaryllis family (Amaryllidaceae). Overall, this research produced a framework that can broadly be applied to the study of other organisms in order to explore more mechanistic-based explanations for how macroevolution took place.

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121 pages
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Specht, Chelsea Dvorak
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Stevenson, Dennis
Frank, Margaret Hannah
Moreau, Corrie
Gandolfo Nixon, Maria Alejandra
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Plant Biology
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Ph. D., Plant Biology
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Doctor of Philosophy
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Government Document
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dissertation or thesis
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