Thesis Title

Epistasis, Mutational Contingency, and the Divergence of Populations Under Uniform Selection

Date of Graduation

Spring 2001


Master of Science in Biology



Committee Chair

John Heywood

Subject Categories



The importance of epistasis in adaptive evolution is not well understood. Epistasis plays a vital role in many models of reproductive isolation, however, and its ubiquity is evidenced by hybrid breakdown in recombinants produced by populations that have diverged. In this thesis I examine the potential for divergence of populations due to a process I call mutational contingency, which is an extension of the Dobzhansky-Muller speciation model to more than two loci. I used computer algorithms to simulate evolution on fitness landscapes that are complex due to epistatic interactions between as many as six loci. Genotypic fitness landscapes were generated using Kauffman's NK model and a model based on the traditional additive ANOVA used for partitioning genotypic variance. I found that epistatic interactions among as few as five loci affecting fitness virtually guarantees divergence of populations, but that random epistasis is unlikely to generate strong reproductive isolation. I propose a model with one major gene and multiple modifier genes that generates fitness landscapes that promote reproductive isolation.


© Michael Dickerson