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Evolution. 2015 May;69(5):1313-20. doi: 10.1111/evo.12645. Epub 2015 Apr 29.

Modeling and quantifying frequency-dependent fitness in microbial populations with cross-feeding interactions.

Author information

1
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, 48824. ribeck@msu.edu.
2
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, 48824. ribeck@msu.edu.
3
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, 48824.
4
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, 48824.

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.

KEYWORDS:

Black Queen interaction; cross-feeding interaction; ecological modeling; fitness measurement; frequency dependence; polymorphism

PMID:
25787308
DOI:
10.1111/evo.12645
[Indexed for MEDLINE]

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