Journal of Molecular Evolution

, Volume 61, Issue 2, pp 171–180 | Cite as

Long-Term Experimental Evolution in Escherichia coli. XIII. Phylogenetic History of a Balanced Polymorphism

  • Daniel E. Rozen
  • Dominique Schneider
  • Richard E. Lenski


We investigated the phylogenetic history of a balanced polymorphism that evolved in an experimental population of Escherichia coli. Previous work showed that two ecologically and morphologically distinct types, designated L (large) and S (small), arose by generation 6000 and coexisted for more than 12,000 generations thereafter. Here, we performed RFLP analyses using Insertion Sequence elements to resolve the phylogenetic history of L and S. Specifically, we sought to determine whether the derived S morph was monophyletic, indicating a long history of coexistence with L or, alternatively, S was repeatedly regenerated from L, indicating a series of periods with only transiently stable coexistence. Phylogenetic analysis of some 200 clones collected throughout the history of this population demonstrates that S is monophyletic. We then performed competition assays using clones of both morphs from different generations to determine whether either or both lineages continued to undergo genetic adaptation. Indeed, both lineages continued to adapt, and their continued evolution contributed to fluctuations in their relative abundance over evolutionary time. Based on their phylogenetic history and independent evolutionary trajectories, S and L fulfill Cohan’s criteria for being different asexual species.


Adaptation Balanced polymorphism Escherichia coli Experimental evolution Insertion sequence Phylogeny Speciation Species concepts 



This collaborative project began in the laboratory of Prof. Michel Blot (Université Joseph Fourier, Grenoble), who died before our work was completed. We dedicate this paper to his memory. We thank V. Cooper, A. de Visser, M. Habets, S. Remold, and two anonymous reviewers for helpful comments on the manuscript and N. Hajela for her valuable assistance in the laboratory. Funding was provided by the U.S. National Science Foundation and by the French CNRS.


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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Daniel E. Rozen
    • 1
  • Dominique Schneider
    • 2
  • Richard E. Lenski
    • 3
  1. 1.Ecology, Evolutionary Biology, and Behavior ProgramMichigan State UniversityEast LansingUSA
  2. 2.Laboratoire Adaptation et Pathogénie des MicroorganismesUniversité Joseph FourierLa TroncheFrance
  3. 3.Department of Microbiology and Molecular GeneticsMichigan State UniversityEast LansingUSA

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