Date of Award

Spring 2011

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Vaughn S Cooper


Phenotypic plasticity, epistasis or both are expected to influence the adaptive value of mutations and, by extension, how organisms adapt to new environments. We investigated interactions among five mutations that arose and fixed in a laboratory-evolved population of E. coli in a variety of different external environments. Overall, we found that positive pleiotropy tended to be positive rather than antagonistic and that epistatic interactions were common regardless of the external environment. The nature of the epistatic interactions depended strongly on the external environment and altered which adaptive paths were selectively accessible. Ultimately, achieving high fitness in a new environment was not due to synergistic interactions occurring between new beneficial mutations. Rather, new mutations that minimize antagonistic epistatic interactions while also improving fitness overall are most favorable. Thus, the fate of a new mutation does not solely depend on its individual fitness effect, but also its genetic and environmental contexts.