The biogeography and origin of New Zealand Sophora (Leguminosae) : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Plant Molecular Genetics at Massey University, New Zealand
The application of DNA sequencing to studies of the biogeography and origin of New Zealand plant groups is illustrated by evolutionary relationships of kowhai (Sophora spp.; sect. Edwardsia; Sophoreae: Papilionoideae: Leguminosae). DNA sequences from an intergene region of the chloroplast atpB-rbcL were determined for l2 species by the use of the polymerase chain reaction. Signals in the molecular data were evaluated using phylogenetic algorithms to reconstruct the evolutionary history of the species. The extremely high genetic similarity between Edwardsia Sophora resulted in an inability to fully resolve the phylogenetic tree. Three hypotheses are presented to account for the patterns of sequence differences between the New Zealand Edwardsia. One proposes a recent origin of Sophora section Edwardsia in New Zealand (4-10 million years ago), with subsequent dispersal of buoyant Sophora microphylla seeds to offshore and oceanic islands, where they might occasionally colonise. A second hypothesis suggests a recent radiation of Sophora microphylla and Sophora prostrata populations during the Pleistocene (0.1 - 1.6 million years ago), but is not well supported by the available sequence data. A third hypothesis proposes that the Lord Howe Island and New Zealand Sophora are derived from a Miocene (5-16 million years ago) oceanic migration of a Chilean ancestor of Sophora section Edwardsia. Predictions of the three hypotheses and strategies to test them are discussed. Some of the conclusions derived from analyses of the chloroplast DNA sequences conflict with those obtained from morphological and chemotaxonomical studies. Analyses of all data sets indicates that the variations in morphology and secondary metabolitic constituents between Sophora prostrata and Sophora microphylla obscures a small amount of genetic diversity. The question of hybrid origins for Sophora microphylla is not supported by tree reconstructions from the molecular data set, and further genetic and ecological studies are required to investigate this.