Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [115]-128).

Forty clones of Gonium pectorale M'uller were crossed in all combinations at 20°C, and the resultant zygotes examined to determine the degree of sexual compatibility within a single population. Clones isolated from the same site but in different years were incompatible, indicating a lack of gene flow between them. Two distinct groups were found within 31 clones isolated from a single mud sample, and all the clones in one were incompatible with all those in the other. However, members of both groups were compatible with those in a third group. The existence of at least two complementary pairs of mating types within a single G. pectorale population, sensu Stein (1958b), is considered in the context of other sexual compatibility results, and is proposed as a reason for the occasional inability to obtain opposite mating types from a mud sample from which only a few clones have been isolated. / Science, Faculty of / Botany, Department of / Graduate

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Les récents progrès en génomique ont conforté la complexité de l’origine des algues; d’un point de vue de la phylogénie des hôtes de l’endosymbiose, les algues forment un groupe évolutif polyphylétique. Les algues vertes forment deux embranchements majeurs : les Streptophyta et les Chlorophyta. Les chlorophytes comprennent la majorité des algues vertes connues et se regroupent en quatre classes. La première, les Prasinophyceae, occupe la position la plus basale, tandis que l’ordre d’embranchement des trois autres classes (Ulvophyceae, Trebouxiophyceae et Chlorophyceae) demeure encore incertain. Pour clarifier les relations évolutives chez les Clorophyceae, huit génomes chloroplastiques appartenant à la lignée des Chlamydomonadales, lignée majeure des Chlorophyceae, ont été séquencés et analysés. Des études phylogénétiques ont confirmé les classifications préétablies et de nouveaux clades se sont vus formés. Les génomes de ces algues chlorophycéennes ont révélé une architecture conservée avec un certain nombre de caractères spécifiques à la classe des Chlamydomonadales. L’analyse de leurs caractères moléculaires a révélé des génomes marqués par la réduction ou le réarrangement de leur répertoire génomique comparativement aux génomes chloroplastiques des algues vertes plus ancestrales. / Recent advances in genome sequencing and analysis have reinforced the complexity of the origin of the green algae. From the point of view of a host endosymbiotic phylogeny, green algae form a polyphyletic evolutionary group. Green algae form two major branches : the Streptophyta and Chlorophyta. Chlorophytes include the majority of green algae known and they are grouped into four classes. The first, that of Prasinophyceae, occupies the most basal position, while the branching order of the other three classes (Ulvophyceae, Trebouxiophycea and Chlorophyceae) remain uncertain. To clarify the evolutionary relationships amongst Chlorophyceae, eight chloroplast genomes belonging to the lineage of Chlamydomonadales, a major clade of Chlorophyceae were sequenced and analyzed. Phylogenetic studies have confirmed the pre-established classifications and new clades were seen to be formed. The genomes of these chlorophyll algae were revealed to be conserved with a number of specific architectural characters of the Chlamydomonadales class. Analysis of their molecular characteristics revealed a genome marked by the reduction or rearrangement of their genomic repertory compared to chloroplast genomes of the ancestral green algae.

This thesis is a study of the evolution and development of the flagellate green algae. The first part is a comparative study of the evolution of body size, multicellularity and segregated soma. The allometry of morphological characters, development, life history and the life cycle are also considered. The second part is an experimental test of the potential role of mutation as a determinant of the course of evolution. Mutation is directional for all the characters studied. The variances and covariances created by mutation are compared to those of 30 species of Volvocaceae; the correspondence between the two depends upon the characted examined. In the third part, the growth of germ cells grown with and without a soma is compared. The response to nutrient concentration of cells grown with an intact soma is steeper than that of cells grown without a soma. This result demonstrates a physiological advantage of soma in Volvox, attributable to a division of labour between 'source' and 'sink'.

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Master of Science / Division of Biology / Bradley J. Olson / Unicellular organisms alter their behavior and morphology in response to environmental stresses, particularly in response to immediate threats to their survival. A common tactic of predator avoidance for unicellular green algae is to aggregate to form groups. We have found that the model unicellular green algae Chlamydomonas reinhardtii forms aggregates in response to the presence of the filter feeding zooplanktonic predator, Daphnia magna. Chalmydomonas is a member of the volvocine algae, a morphologically diverse group of closely related green algae that is often used to study multicellular development. We have characterized aggregation in Chlamydomonas reinhardtii and found that it is rapid, transient and induced by signals originating from the Daphnia predators. To understand the genetic basis of cooperative aggregation we used an RNA-seq approach. RNA-seq characterized the transcriptomic response by Chlamydomonas during aggregation, and we identified 131 genes are significantly differentially expressed between predated and unpredated cultures of Chlamydomonas. Several candidate genes were characterized based on existing annotations, evolutionary history and expression profile. Evolutionary relationships between candidate aggregation genes in Chlamydomonas and their orthologs in multicellular Volvocales suggest a possible role of aggregation genes in multicellular development. Our results demonstrate that Chlamydomonas dynamically alters its morphology based on its environment and identify several candidate genes for aggregation and multicellular development.