Systematics and evolutionary diversification in the species-rich neotropical tree genus Swartzia (Leguminosae-Papilionoideae)

Neotropical rainforests are the most species-rich ecosystems on earth and are dominated by trees in terms of structure, productivity, and botanical species richness. The evolutionary mechanisms that underlie diversification in Neotropical trees are largely unknown. Hypotheses range from vicariant speciation via historical climatic and geologic changes to recent ecological diversification. Efforts to test these hypotheses are plagued by insufficient biological data for large Neotropical tree clades. This dissertation marks the beginning of a long-term effort to build a variety of biological datasets for the Neotropical tree genus Swartzia (ca. 180 species), with the aim of testing diversification-related hypotheses.; A molecular phylogenetic study of the "swartzioid clade" was performed to examine relationships within Swartzia and among related genera. The analyses resolved a "core swartzioid clade" consisting of Swartzia, Bocoa and Candolleodendron. Swartzia itself, excluding S. panamensis, was supported as monophyletic. The analyses identified 11 major subclades of Swartzia, none of which correspond exactly to published taxa.; The phylogenetic analyses and phylogenetic dating formed the basis of a historical biogeographic study. The results suggest that Swartzia originated in the early Miocene, probably in South America. The presence of Swartzia in Central America and eastern Brazil resulted mostly from migrations from South America, which left strong phylogenetic handprints. In contrast, there is no correlation between phylogeny and geographical distributions across most of Amazonia and the Guianas.; A molecular phylogeographic study of the Central American apetalous clade of Swartzia (ca. 8 species) was performed to explore diversification within and among closely related species. A network approach was adopted to examine relationships among chloroplast halplotypes. Marked interspecific genetic divergences and mostly non-overlapping species distributions suggest a history of allopatric speciation. The locations of geographic barriers to gene flow often correlate with species boundaries and genetic divergences. In contrast to the expectation that gene flow predominates in tropical trees, the vast majority of intraspecific genetic variation is due to differences between highly subdivided populations.; Taken together, these studies illustrate the usefulness of an approach to studying tropical tree diversification that emphasizes the collection and integration of a variety of biological data for species-rich clades.