Date of Award

Spring 2009

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Vaughn Cooper


Understanding the distribution of beneficial mutations is relevant to the understanding of virtually all aspects of the adaptive process. Data describing this distribution are limited, but even less well understood are the pleiotropic effects of adaptive mutations. Yet, the pleiotropy of beneficial mutations may play a role in numerous biological processes. In this thesis, we address this problem by measuring the distribution of beneficial mutations and their pleiotropic effects using mutants of Burkholderia cenocepacia and Escherichia coli. The fitness of each mutant was measured relative to its progenitor in several novel environments. We found that the effects of beneficial mutations are best explained by an exponential distribution. We also found that most beneficial mutations increased fitness in alternative environments, indicating positive pleiotropy. Thus, the early steps of adaptation appear to generally expand niche breadth, with mutations of larger benefit producing greater improvements in foreign environments.