, Volume 139, Issue 5, pp 677–684 | Cite as

On the nature of species: insights from Paramecium and other ciliates



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 defines a species as a natural group of organisms that is reproductively isolated from other such groups. Here we synthesize nearly a century of research on the ciliate genus Paramecium that highlights the shortcomings of our prevailing notions on the nature of species. In this lineage, there is discordance between morphology, mating behavior, and genetics, features assumed to be correlated, at least after sufficient time has passed, under all species concepts. Intriguingly, epigenetic phenomena are well documented in ciliates where they influence features such as germline/soma differentiation and mating type determination. Consequently, we hypothesize that divergence within ciliate populations is due to a dynamic interaction between genetic and epigenetic factors. The growing list of examples of epigenetic phenomena that potentially impact speciation (i.e. by influencing the dynamics of sex chromosomes, fate of hybrids, zygotic drive and genomic conflicts) suggests that interactions between genetics and epigenetics may also drive divergence in other eukaryotic lineages.


Species concepts Paramecium Epigenetics Ciliates Molecular evolution 



L. A. K. is extremely grateful to R.G. Harrison for the excellent training and continued support. L. A. K. is also supported by grants from the National Science Foundation (DEB RUI:0919152, DEB 043115, DEB 0816828) and National Institutes of Health (1R15GM081865-01).


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  1. 1.Department of Biological SciencesSmith CollegeNorthamptonUSA
  2. 2.Program in Organismic and Evolutionary BiologyUniversity of MassachusettsAmherstUSA

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