Maintaining a behaviour polymorphism by frequency-dependent selection on a single gene


Accounting for the abundance of genetic variation in the face of natural selection remains a central problem of evolutionary biology1,2. Genetic polymorphisms are constantly arising through mutation, and although most are promptly eliminated3, polymorphisms in functionally important traits are common. One mechanism that can maintain polymorphisms is negative frequency-dependent selection on alternative alleles, whereby the fitness of each decreases as its frequency increases4,5. Examples of frequency-dependent selection are rare, especially when attempting to describe the genetic basis of the phenotype under selection. Here we show frequency-dependent selection in a well-known natural genetic polymorphism affecting fruitfly foraging behaviour. When raised in low nutrient conditions, both of the naturally occurring alleles of the foraging gene (fors and forR) have their highest fitness when rare—the hallmark of negative frequency-dependent selection. This effect disappears at higher resources levels, demonstrating the role of larval competition. We are able to confirm the involvement of the foraging gene by showing that a sitter-like mutant allele on a rover background has similar frequency-dependent fitness as the natural sitter allele. Our study represents a clear demonstration of frequency-dependent selection, and we are able to attribute this effect to a single, naturally polymorphic gene known to affect behaviour.

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Figure 1: The effects of frequency and nutrient level on rover and sitter fitness.
Figure 2: The fitnesses of the rover strain and sitter mutants when raised in lower nutrient levels and over a range of allele frequencies (3:1, 1:1, 1:3).
Figure 3: The fitnesses of unmarked rovers and sitters when raised in lower nutrient levels and over a range of allele frequencies (3:1, 1:1, 1:3).


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We thank C. Reaume, S. Douglas and D. Rukavina for assistance with experiments. We also thank D. Gwynne, J. Anderson, H. Rodd, J. Levine, K. Judge, C. Kent, C. Riedl, A. Agrawal, M. Kasumovic and members of the Sokolowski laboratory for discussions and comments. This research was supported by Natural Sciences and Engineering Research Council (NSERC) grants and Canada Research Chairs to M.B.S. and L.R.

Author Contributions M.J.F., M.B.S. and L.R. designed and analysed the experiments. M.J.F. conducted the experiments with assistance from E.F. M.J.F with M.B.S. and L.R. wrote the paper, and all authors discussed and commented on the manuscript during revisions.

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Correspondence to Marla B. Sokolowski.

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Fitzpatrick, M., Feder, E., Rowe, L. et al. Maintaining a behaviour polymorphism by frequency-dependent selection on a single gene. Nature 447, 210–212 (2007).

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