Evolution of Jatropha : phylogenetics, biogeography, and phylogeography




LeClear, Nathan Michael

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The genus Jatropha (Euphorbiaceae) is comprised of approximately 180 species of flowering plants adapted to arid and semi arid climates in tropical regions around the world. As the evolutionary relationships within this group have not been tested using molecular phylogenetic approaches, I used a combination of traditional molecular markers and genomic data generated from restriction site-associated DNA sequencing (RADseq) for this purpose. Using this phylogeny, I answered questions of trends in morphological evolution in the neotropical species of Jatropha, and explored potential causes of missing data in RADseq datasets. I reconstructed the biogeographic history of Jatropha at the global scale to test hypotheses of vicariance and dispersal pertaining to pantropical disjunct groups. I also investigated the impact of tectonic events on diversification of Jatropha within Mesoamerica, and tested standing hypotheses about geographic structure in lineages endemic to seasonally dry tropical forests. Using J. cardiophylla as a model, I looked for evidence of Pleistocene refugia in the interior Sonoran Desert using RADseq and ecological niche modeling. Jatropha was found to be monophyletic based upon traditional markers, and relationships within Jatropha were resolved with RADseq data. Evolutionary analyses indicated the ancestor of Jatropha was a shrub bearing a tricarpellate fruit. Jatropha originated in the Neotropics and arrived in Africa via at least two long distance dispersal events. Tectonic events in Mesoamerica impacted diversification of Jatropha through both vicariance events and by preventing dispersal between areas. Mixed evidence was found in support of the hypothesis that seasonally dry tropical forest lineages are dispersal limited and primarily experience in situ diversification. Genetic analysis of J. cardiophylla showed that this species consists of two genetically distinct, yet geographically overlapping lineages. Ages of coalescence for each lineage predate the Last Glacial Maximum. Niche modeling did not identify obvious Pleistocene refugia, but somewhat aligned with spatial patterns of genetic variation. It appears that J. cardiophylla has responded to multiple rounds of climate change in the Sonoran Desert, and that different lineages may have responded differently. The sum of this work represents a significant contribution to our understanding of the evolution of Jatropha at multiple scales.



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