Originally published as Genetics Published Articles Ahead of Print on May 4, 2007.

Genetics, Vol. 176, 1729-1740, July 2007, Copyright © 2007
doi:10.1534/genetics.107.073072

Frequency-Dependent Selection and the Maintenance of Genetic Variation: Exploring the Parameter Space of the Multiallelic Pairwise Interaction Model

Meredith V. Trotter1 and Hamish G. Spencer

Department of Zoology, Allan Wilson Centre for Molecular Ecology and Evolution, University of Otago, Dunedin 9054, New Zealand

1 Corresponding author: Department of Zoology, Allan Wilson Centre for Molecular Ecology and Evolution, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
E-mail: mer.trotter{at}gmail.com

When individuals' fitnesses depend on the genetic composition of the population in which they are found, selection is then frequency dependent. Frequency-dependent selection (FDS) is often invoked as a heuristic explanation for the maintenance of large numbers of alleles at a locus. The pairwise interaction model is a general model of FDS via intraspecific competition at the genotypic level. Here we use a parameter-space approach to investigate the full potential for the maintenance of multiallelic equilibria under the pairwise interaction model. We find that FDS maintains full polymorphism more often than classic constant-selection models and produces more skewed equilibrium allele frequencies. Fitness sets with some degree of rare advantage maintained full polymorphism most often, but a wide variety of nonobvious fitness patterns were also found to have positive potential for polymorphism. An example is put forth suggesting possible explanations for multiallelic polymorphisms maintained despite positive FDS on individual alleles.