Evolution
ORIGINAL ARTICLE

Evolution under pH stress and high population densities leads to increased density‐dependent fitness in the protist Tetrahymena thermophila

Felix Moerman

Corresponding Author

E-mail address: felix.moerman@ieu.uzh.ch

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, Dübendorf, CH‐8600 Switzerland

ISEM, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France

Swiss Institute of Bioinformatics, Quartier Sorge—Bâtiment Génopode, Lausanne, 1015 Switzerland

Email:

felix.moerman@ieu.uzh.ch

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Angelina Arquint

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

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Stefanie Merkli

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

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Andreas Wagner

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

Swiss Institute of Bioinformatics, Quartier Sorge—Bâtiment Génopode, Lausanne, 1015 Switzerland

The Santa Fe Institute, Santa Fe, New Mexico, 87501 USA

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Florian Altermatt

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, Dübendorf, CH‐8600 Switzerland

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Emanuel A. Fronhofer

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH‐8057 Switzerland

Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, Dübendorf, CH‐8600 Switzerland

ISEM, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France

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First published: 15 January 2020
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Abstract

Abiotic stress is a major force of selection that organisms are constantly facing. While the evolutionary effects of various stressors have been broadly studied, it is only more recently that the relevance of interactions between evolution and underlying ecological conditions, that is, eco‐evolutionary feedbacks, have been highlighted. Here, we experimentally investigated how populations adapt to pH‐stress under high population densities. Using the protist species Tetrahymena thermophila, we studied how four different genotypes evolved in response to stressfully low pH conditions and high population densities. We found that genotypes underwent evolutionary changes, some shifting up and others shifting down their intrinsic rates of increase (r0). Overall, evolution at low pH led to the convergence of r0 and intraspecific competitive ability (α) across the four genotypes. Given the strong correlation between r0 and α, we argue that this convergence was a consequence of selection for increased density‐dependent fitness at low pH under the experienced high density conditions. Increased density‐dependent fitness was either attained through increase in r0, or decrease of α, depending on the genetic background. In conclusion, we show that demography can influence the direction of evolution under abiotic stress.

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