title: Modeling and quantifying frequency-dependent fitness in microbial populations with cross-feeding interactions.
abstract: Coexistence of two or more populations by frequency-dependent selection is common in nature, and it often arises even in well-mixed experiments with microbes. If ecology is to be incorporated into models of population genetics, then it is important to represent accurately the functional form of frequency-dependent interactions. However, measuring this functional form is problematic for traditional fitness assays, which assume a constant fitness difference between competitors over the course of an assay. Here, we present a theoretical framework for measuring the functional form of frequency-dependent fitness by accounting for changes in abundance and relative fitness during a competition assay. Using two examples of ecological coexistence that arose in a long-term evolution experiment with Escherichia coli, we illustrate accurate quantification of the functional form of frequency-dependent relative fitness. Using a Monod-type model of growth dynamics, we show that two ecotypes in a typical cross-feeding interaction-such as when one bacterial population uses a byproduct generated by another-yields relative fitness that is linear with relative frequency.
authors: Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, 48824. ribeck@msu.edu.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, 48824. ribeck@msu.edu.
authors: Noah
authors: N
authors: Ribeck
authors: Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, 48824.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, 48824.
authors: Richard E
authors: RE
authors: Lenski
mesh_terms: D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics; D019143:Evolution, Molecular; D056084:Genetic Fitness; D008957:Models, Genetic; D009245:NADH Dehydrogenase / Q000235:genetics; D011110:Polymorphism, Genetic
chemical_list: D029968:Escherichia coli Proteins; D009245:NADH Dehydrogenase; C476247:NuoM protein, E coli
keywords: Black Queen interaction; cross-feeding interaction; ecological modeling; fitness measurement; frequency dependence; polymorphism