Dissertation Research: Evolution of Breeding Systems in Hawaiian Psychotria: A Phylogenetic Approach

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SYTSMA 9423590 This award will support a study of the Hawaiian species of Psychotria and their relatives, including (1) a molecular phylogenetic anaylsis and (2) comparative analysis of changes in the breeding breeding system among different lineages. Due to lack of good morphological characters, the infra-generic classification of Psychotria has not been resolved and the genus has only been treated at a regional level. In particular the relationship(s) of the Hawaiian members to the rest of the genus is in question. There is considerable debate over whether the Hawiian species of this genus really constitute a monophyletic group (a natural, related unit) or are the result of multiple introductions to the islands. This study will determine the number of independent introductions of Psychotria to Hawaii. Molecular data from two sources, nuclear ribosomal ITS and chloroplast (matK) DNA sequences will be analyzed in a phylogenetic context to clarify these issues. The information provided by the phylogeny will be used to infer patterns of colonization and speciation within and between islands. Preliminary results indiacte that patterns of colonization and speciation of Psychotria in the Hawiian islands do not confrom to previously established patterns for other groups of organisms studied in which oldest islands contain basal elements of radiations. The Hawaiian Psychotria provide an ideal model system to test theories on the origin and maintenance of plant breeding systems on islands. The Hawaiian Psychotria are one of only six known cases where dicliny (male and female organs in separate flowers) has arisen from distyly (single flowers including both male and female parts but with individual flowers having an exaggeration of the organs of one sex). Field studies will be undertaken to formally characterize the breeding systems of different species at a population level and examine characteristics of pollinator systems for the Hawaiian species of Psychotria. The phylogeny generated in one part of the study will provide the necessary historical background to examine patterns and processes in the development of different breeding systems. The potential occurrence of multiple introductions to the islands may provide a unique opportunity to examine selective forces in the origin of dicliny in replicate systems. %%% This study will clarify the relationships of a group of plants occurring in the Hawaiian islands. It will also address important questions concerning the breeding systems of colonizing organisms that may be relevant to issues involving introduced pest species in other groups. ***