Doctor of Philosophy
Biology, Plant Systematics
Date of Defense
P. F. Stevens
Despite a large accumulation of evidence on the high richness of plant species in the mountains of South America, little is known about the historical underpinnings of this diversity. To contribute to our understanding of the origin and diversification of plant species in these mountains, I analyzed geographic patterns of variation in molecular and phenotypic characters for the genus Escallonia L.f. (Escalloniaceae), a group of shrubs widespread in montane habitats in South America. Molecular phylogenetic analyses using chloroplast and nuclear loci revealed i) that Escallonia is monophyletic, ii) a remarkable level of geographical phylogenetic structure, and iii) a widespread absence of species-level monophyly. These results are consistent with the hypothesis that geography played an important role early in the history of Escallonia by separating populations, which later diversified rapidly and/or recently in isolation. To evaluate whether the lack of monophyly could reflect problems with species boundaries, I present a new statistical approach that uses morphological and geographical data to i) weigh the strength of the evidence to support the hypothesis that species are separated by morphological gaps, and ii) examine if gaps could be explained by an alternative hypothesis of geographic differentiation within a single species rather than by a hypothesis of a species boundary. Analyses of morphological measurements using this approach provided support to several of the current hypotheses of species boundaries within Escallonia, suggesting that neutral molecular variation and phenotypic variation are not evolving in concert. Analyses of bioclimatic data provided further evidence that most species differed in their climatic niche, and thus display differences in their present day selective regimes. By integrating molecular, morphological and bioclimatic analyses, I provide evidence to infer that most species (71%) within Escallonia represent distinct evolutionary lineages on independent evolutionary trajectories. A new species of Escallonia is described. Data exploration suggests that environmental gradients may have played an important role in recent speciation events. Taken together, these results illustrate the usefulness of an approach to studying plant diversification that emphasizes the collection and integration of a variety of biological data to better understand the origin and evolution of species.
Zapata, Felipe, "Phylogenetics and diversification of Escallonia (Escalloniaceae)" (2011). Dissertations. 438.