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UBC Theses and Dissertations

Using a low-copy nuclear gene (phosphoglycerate kinase; PGK) to explore the phylogeny of the aquatic plant family Hydatellaceae (Nymphaeales) Lin, Qianshi


Hydatellaceae are a small aquatic family of 12 species related to water lilies, part of the ANITA grade of angiosperms. Our current understanding of phylogenetic relationships in the family comes from several plastid genes and nuclear ITS data. These data sets are generally highly congruent, and lend support to the monophyly of multiple species. However, the published nuclear ITS tree was unrooted (outgroups were too distant to align), and there were several minor phylogenetic conflicts between plastid and ITS gene trees for three closely related species, Trithuria bibracteata, T. occidentalis, and T. submersa; two of these species were also not reciprocally monophyletic in individual gene trees. The position of T. occidentalis was also based on very limited plastid data, and there was no molecular evidence to link staminate and pistillate individuals in this species. To further clarify phylogenetic relationships and species boundaries, I recovered two copies of nuclear-encoded phosphoglycerate kinase (PGK) gene from taxa in Hydatellaceae and several water lilies. I reconstructed the history of the PGK duplication in angiosperms as a whole. I also added plastid data from additional populations of several species, and estimated the dated species tree using a Bayesian multispecies coalescent approach to reconcile different gene trees. The angiosperm-level PGK gene tree indicated that the duplication of PGK gene may have happened around the origin of angiosperms. The root of Hydatellaceae implied by concatenated nuclear PGK matches that inferred from plastid data. Trithuria occidentalis is clearly placed in sect. Trithuria, and staminate and pistillate individuals of this species are linked together using new evidence from the plastid and PGK genes. Phylogenetic relationships inferred using each PGK copy are consistent with the sectional relationships inferred using plastid and ITS data, with less sharply defined species boundaries. I also explore the possibility here that some of the incongruence that I observed between individual genes trees and in inferred species trees is a consequence of additional minor gene duplications or polyploidization/introgression events.

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