A dynamical limit to evolutionary adaptation

Author:

Melissa Matthew J.1234,Desai Michael M.1234ORCID

Affiliation:

1. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138

2. Department of Physics, Harvard University, Cambridge, MA 02138

3. Quantitative Biology Initiative, Harvard University, Cambridge, MA 02138

4. National Science Foundation (NSF)-Simons Center for Mathematical and Statistical Analysis of Biology, Harvard University, Cambridge, MA 02138

Abstract

Natural selection makes evolutionary adaptation possible even if the overwhelming majority of new mutations are deleterious. However, in rapidly evolving populations where numerous linked mutations occur and segregate simultaneously, clonal interference and genetic hitchhiking can limit the efficiency of selection, allowing deleterious mutations to accumulate over time. This can in principle overwhelm the fitness increases provided by beneficial mutations, leading to an overall fitness decline. Here, we analyze the conditions under which evolution will tend to drive populations to higher versus lower fitness. Our analysis focuses on quantifying the boundary between these two regimes, as a function of parameters such as population size, mutation rates, and selection pressures. This boundary represents a state in which adaptation is precisely balanced by Muller’s ratchet, and we show that it can be characterized by rapid molecular evolution without any net fitness change. Finally, we consider the implications of global fitness-mediated epistasis and find that under some circumstances, this can drive populations toward the boundary state, which can thus represent a long-term evolutionary attractor.

Funder

National Science Foundation

HHS | National Institutes of Health

Publisher

Proceedings of the National Academy of Sciences

Reference71 articles.

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