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Form and structure of variation within lineages of Wyethia and Balsamorhiza Robson, Kathleen Anne


This study illustrates a method of comparing morphological aspects of within-species variation to speciation events within larger lineages in an effort to compare the variation which has arisen as a result of ontogeny to that which has been expressed during phylogeny. The source and structure of variation at these different levels of biological organization in the genera Wyethia and Balsamorhiza (Asteraceae, Heliantheae) were studied using different analytical techniques. This approach attempts to illustrate how a deeper understanding of the nature of biological change over time might be gained when these hierarchically related levels of variation are analyzed with appropriate techniques and compared. This study demonstrates a new and potentially valuable application of different methodologies to the examination of evolutionary processes. The relationships within and between Wyethia and Balsamorhiza have presented problems in the past and an attempt was made to clarify the evolutionary patterns among species. The methods of phylogenetic systematics were employed in order to gain a better understanding of these historical relationships. It was found that taxonomic outgroups were valuable mainly in their ability to delimit small clades, which were then used as functional outgroups. The use of functional outgroups permitted a larger number of variables to be used, including a more detailed set of morphological characters and data derived from flavonoid chemistry. More data and the rest of the taxa are required before relationships among all species can be fully clarified. Small monophyletic groups of species were identified and confirmed from the results of the cladistic analyses. These clades were used to provide a framework within which a the results of the analysis of within-species variation could be viewed. The second part of this study examined morphological variation based on measurements taken from individual plants. Techniques based on principal components analysis were employed to explore this variation for structure and source. Variation in separate data sets describing heads, shoots and leaves was apportioned to taxonomic levels by analysis of variance of PCA scores. Most of the variation was attributable to groups of related species (genera and sections) or to the species themselves. Populations accounted for little of the overall variation. 95% confidence ellipse statistics were calculated for point swarms describing each species. The ellipse results were translated into graphic representations of variation and variable correlation structure from the head, shoot and leaf data for each species. These graphics were then projected onto the branch tips of cladograms so that within-species variation could be compared among species and lineages composed of species. When within-species variation was examined for changes in source and structure it was found that much of it appears to be attributable to the history of a clade. In addition, some unique and unexpected aspect of variation within each species is always apparent and may be related to the speciation event itself. That is, the nature and source of ontogenetic variation appears to be related to phylogenetic variation. The variation quantified from different hierarchical levels of biological organization appears to demonstrate similar properties of historical conservatism and emergence. These results are examined in the light of current theories which address the nature of biological change over time and are found to be best explained by a new theory of evolution based on nonequilibrium thermodynamics.

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