UBC Theses and Dissertations

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UBC Theses and Dissertations

Population differentiation of two sympatric species of red algae, mazzaella splendens and mazzaella linearis, in Barkley Sound, Columbia, Canada Shaughnessy, Frank James


The thesis objective was to study algal population differentiation by focusing on two species, Mazzaella splendens (Setchell et Gardner) Hommersand and Mazzaella linearis (Setchell et Gardner) Fredericq (Gigartinaceae, Rhodophyta). Chapter 2 checked the accuracy of the resorcinol test for identifying isomorphic gametophytes and sporophytes in the Gigartinaceae. Sources of variation examined were methods of thallus storage, location and tissue type, species and season. Vegetative phases of M. splendens and M. linearis, and most other taxa examined, could be identified with confidence. The objective of Chapter 3 was to describe the correlation between Mazzaella G. DeToni f. and the low intertidal environment in Barkley Sound. The secondary objective was to identify the species of Mazzaella in this environment. Dimensions for stipe length and blade width indicated that thalli from sites exposed to low and intermediate wave exposure were M. splendens whereas thalli at the high exposure site were M. linearis. The two species were sympatric and significant correlations of morphological characters to environment suggests that some characters are adaptive. In Chapter 4, the objective was to determine if morphological variation of M. splendens and M. linearis is due to genetic differentiation or phenotypic plasticity. Holdfasts of each species were transplanted into common gardens and morphology and thallus mass were compared one year later. Results indicated that species morphologies are due to genetic differentiation and thallus mass responses for M. linearis indicated that it was not completely able to physiologically acclimate to the low exposure site. Chapter 5 ascertained if selection is maintaining the genetic differentiation between M. splendens and M. linearis. Survivorship data indicate that, at the high wave exposure site of M. linearis, it is probably high water velocities selecting against M. splendens. Factors that eventually selected against M. linearis at the low exposure site are less clear. In combination with studies outside of my thesis that reinforce the idea that some characters are adaptive, and that the two species are closely related, my thesis indicates that differences of vegetative characters, and possibly physiological tolerances, are products of population differentiation due to adaptive radiation.

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