A Molecular Phylogenetic Study of Historical Biogeography and the Evolution of Self-Incompatibility RNases in Indian Ocean Coffea (Rubiaceae)

Abstract

<p>A fundamental goal in the diverse field of evolutionary biology is reconstructing the historical processes that facilitated lineage diversification and the current geographic distribution of species diversity. Oceanic islands provide a view of evolutionary processes that may otherwise be obscured by the complex biogeographic histories of continental systems, and have thus provided evolutionary biology with some of its most lasting and significant theories. The Indian Ocean island of Madagascar is home to an extraordinarily diverse and endemic biota, and reconstructing the historical processes responsible for this diversity has consumed countless academic careers. While the flowering plant genus <italic>Coffea</italic> is but one lineage contributing to Madagascar's staggering floral diversity, it is representative of the common evolutionary theme of adaptive radiation and local endemism on the island. In this dissertation, I employ the genus <italic>Coffea</italic> as a model for understanding historical biogeographic processes in the Indian Ocean using methods of molecular phylogenetics and population genetics. In the molecular phylogenetic study of <italic>Coffea</italic> presented in chapter 2, I show that Madagascan <italic>Coffea</italic> diversity is likely the product of at least two independent colonization events from Africa, a result that contradicts current hypotheses for the single origin of this group. </p><p>Species of <italic>Coffea</italic> are known to exhibit self-incompatibly, which can have a dramatic affect on the geographic distribution of plant genetic diversity. In chapter 3, I identify the genetic mechanism of self-incompatibility in <italic>Coffea</italic> as homologous to the canonical eudicot S-RNase system. Baker's Rule suggests that self-incompatible lineages are very unlikely to colonize oceanic islands, and in chapter 4, I test this hypothesis by characterizing the strength of self-incompatibility and comparing S-RNase polymorphism in <italic>Coffea</italic> populations endemic to isolated Indian Ocean islands (Grande Comore and Mauritius) with that of Madagascan/African species. My findings suggest that while island populations show little evidence for genetic bottleneck in S-RNase allelic diversity, Mauritian endemic <italic>Coffea</italic> may have evolved a type of "leaky" self-incompatibility allowing self-fertilization at some unknown rate. Through the application of traditional phylogenetic methods and novel data from the self-incompatibly locus, my dissertation contributes a wealth of new information regarding the evolutionary and biogeographic history of <italic>Coffea</italic> in the Indian Ocean.</p>