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Publication Date


Document Type

Honors Project


Biological Sciences


Paramecium aurelia-Phylogeny-Molecular aspects, Paramecium aurelia-Variation, Tetrahymena-Phylogeny-Molecular aspects, Tetrahymena-Variation, Ciliates, Species diversity, Mitochondrial DNA, Molecular evolution, Paramecium aurelia-Evolution, Tetrahymena-Evolution, Species concept


The multiple species concepts currently in use by the scientific community (e.g. morphological, biological, phylogenetic) are united in that they all aim to capture the process of divergence between populations. For example, the Biological Species Concept (BSC) defines a species as a natural group of organisms that is reproductively isolated from other such groups. Here I synthesize nearly a century of research on two ciliate genera, Paramecium and Tetrahymena that challenge the prevailing notions on the nature of species. In these taxa, there is discordance between morphology, mating behavior, and genetics, features that are assumed to be correlated under the BSC and other contemporary species concepts. Intriguingly, epigenetic phenomena are a prominent force within ciliates. One such instance of epigenetic influence is the determination of mating type. Consequently, epigenetic phenomena likely influence the processes of divergence. Current conceptualization of species does not take into account epigenetic processes and therefore fails to capture the evolutionary history of ciliates and likely other eukaryotic lineages. I suggest that the complex evolutionary patterns of ciliates are not exceptions to the rule but rather vivid examples of the complexity of life and the dynamism of evolution.




[154] p. : ill. (chiefly col.) Honors Project-Smith College, Northampton, Mass., 2010. Includes bibliographical refernces (p. 18-21, 54-60)