Gregory Lang, Ph.D. Assistant Professor, Department of Biological Sciences, Lehigh University

Epistatic Interactions and Constraints on Evolutionary Outcomes in Yeast Experimental Evolution

Abstract

In his 1989 book, Wonderful Life, Stephen Jay Gould proposed the following thought experiment. Rewind the “tape of life” and let evolution play out a second time. In doing so, does the replay produce anything like what we see today? In other words, is evolution reproducible, or do chance events (seemingly inconsequential at the time) cause evolutionary paths to diverge, producing wildly different outcomes? With advances in high-throughput biology, we can perform Gould’s thought experiment in the laboratory by initiating hundreds—or thousands—of identical populations and observing the distribution of evolutionary outcomes. Such experiments demonstrate that replicate populations tend to find similar (but not identical) solutions to the same selective pressure. The degree to which evolutionary outcomes are reproducible depends critically on underlying parameters that are largely unknown, in particular, the distribution of fitness effects and epistatic interactions. The goal of this proposal is to combine high-throughput experimental evolution with the tools of quantitative genetics to measure quantitatively and comprehensively the distributions of these key parameters and to assess the relative roles of chance and determinism in governing evolutionary outcomes. These results will advance a fundamental understanding of how evolution chooses among a vast number of possible paths.

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