Genetics, Vol. 162, 485-499, September 2002, Copyright © 2002

Enzyme Kinetics, Substitutable Resources and Competition: From Biochemistry to Frequency-Dependent Selection in lac

Mark Lunzera, Arvind Natarajana, Daniel E. Dykhuizenb, and Antony M. Deana,c
a BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108,
b Department of Ecology and Evolution, SUNY, Stony Brook, New York 11794
c Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota 55108

Corresponding author: Antony M. Dean, 240 Gortner Laboratories, 1479 Gortner Ave., St. Paul, MN 55108., adean{at}biosci.umn.edu (E-mail)

Communicating editor: C.-I WU

Trade-offs in catalytic efficiency at the lac permease of Escherichia coli produce alleles with different substrate specializations that are selectively favored on different galactosides. We show that differential resource utilization during competition for mixtures of galactosides produces frequency-dependent selection at lac. However, the polymorphism is protected only in a narrow range of galactoside ratios despite intense selection on the pure galactosides. Hence, stabilizing frequency-dependent selection protecting natural allozyme polymorphisms through differential resource utilization will be sporadic and ephemeral in randomly changing environments. A comparison of predictions, based on first principles, with experimental outcomes reveals an additional, unanticipated source of weak selection.




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