9 December 2016
Nicolas Buchler
Department of Biology
Duke University
It is believed that epigenetic systems (i.e. bistable, molecular systems built from self-reinforcing feedback loops) first emerged during the evolution of single-cell organisms adapting to fluctuating environments. This has been exhaustively studied using simple models. However, many of these models assumed the pre-existence of an epigenetic switch and did not explicitly include genetic mutation as a competing process. Thus, the conditions under which epigenetic switches emerge and outcompete adaptation through genetic mutation (a primary force in evolution) remain to be elucidated.
In this talk, I will present our results using a mechanistic model of a self-activating genetic circuit, which can both adapt genetically and exhibit epigenetic switching. In silico evolution experiments of an evolving population in a fluctuating environment elucidated a gradual trade-off between minimizing the adaptation time after each environmental transition and increasing the robustness of the phenotype during constant environments. Epigenetic switches were favored in fast-fluctuating environments because they adapt quickly, whereas genetic adaptation was favored in slowly fluctuating environments. We also correct a misconception that epigenetic switches are accidental by-products of selection for increased nonlinearity and evolvability. This work is the research of Mariana Gomez-Schiavon, a graduate student in my lab.