title: Size evolution in microorganisms masks trade-offs predicted by the growth rate hypothesis.
abstract: Adaptation to local resource availability depends on responses in growth rate and nutrient acquisition. The growth rate hypothesis (GRH) suggests that growing fast should impair competitive abilities for phosphorus and nitrogen due to high demand for biosynthesis. However, in microorganisms, size influences both growth and uptake rates, which may mask trade-offs and instead generate a positive relationship between these traits (size hypothesis, SH). Here, we evolved a gradient of maximum growth rate (μmax) from a single bacterium ancestor to test the relationship among μmax, competitive ability for nutrients and cell size, while controlling for evolutionary history. We found a strong positive correlation between μmaxand competitive ability for phosphorus, associated with a trade-off between μmaxand cell size: strains selected for high μmaxwere smaller and better competitors for phosphorus. Our results strongly support the SH, while the trade-offs expected under GRH were not apparent. Beyond plasticity, unicellular populations can respond rapidly to selection pressure through joint evolution of their size and maximum growth rate. Our study stresses that physiological links between these traits tightly shape the evolution of competitive strategies.
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS, IRD, EPHE, Faculté des Sciences de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France isabelle.gounand@eawag.ch.|Département de Biologie, Université du Québec à Rimouski, Rimouski, Canada.|Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.|Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Isabelle
authors.identifier: 0000-0002-0675-3973
authors.initials: I
authors.lastname: Gounand
authors.affiliation: INRA -UMR Eco&Sols - Bat 12, 2 Place Viala, 34060 Montpellier cedex 1, France.
authors.forename: Tanguy
authors.initials: T
authors.lastname: Daufresne
authors.affiliation: Département de Biologie, Université du Québec à Rimouski, Rimouski, Canada.
authors.forename: Dominique
authors.identifier: 0000-0002-4498-7076
authors.initials: D
authors.lastname: Gravel
authors.affiliation: MARBEC (MARine Biodiversity Exploitation and Conservation), UMR IRD-CNRS-UM-IFREMER 9190, Université Montpellier, CC 093, 34095 Montpellier Cedex 5, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Bouvier
authors.affiliation: MARBEC (MARine Biodiversity Exploitation and Conservation), UMR IRD-CNRS-UM-IFREMER 9190, Université Montpellier, CC 093, 34095 Montpellier Cedex 5, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Bouvier
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS, IRD, EPHE, Faculté des Sciences de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.|UMR MIVEGEC IRD-CNRS-Université de Montpellier, Centre IRD de Montpellier, Montpellier, France.
authors.forename: Marine
authors.identifier: 0000-0002-0708-9234
authors.initials: M
authors.lastname: Combe
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS, IRD, EPHE, Faculté des Sciences de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Gougat-Barbera
authors.affiliation: Laboratoire d'Ecologie Microbienne, Université de Lyon, Université Lyon 1, CNRS, INRA, UMR CNRS 5557, UMR INRA 1418, Bâtiment Gregor Mendel, 16, rue Raphael Dubois, 69622 Villeurbanne Cedex, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Poly
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS, IRD, EPHE, Faculté des Sciences de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
authors.forename: Clara
authors.initials: C
authors.lastname: Torres-Barceló
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS, IRD, EPHE, Faculté des Sciences de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.|MARBEC (MARine Biodiversity Exploitation and Conservation), UMR IRD-CNRS-UM-IFREMER 9190, Université Montpellier, CC 093, 34095 Montpellier Cedex 5, France.
authors.forename: Nicolas
authors.identifier: 0000-0003-1840-6984
authors.initials: N
authors.lastname: Mouquet
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D005075:Biological Evolution; D009584:Nitrogen / Q000502:physiology; D010641:Phenotype; D010758:Phosphorus / Q000502:physiology; D011551:Pseudomonas fluorescens / Q000166:cytology* / Q000235:genetics*
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: Pseudomonas fluorescens; bacteria; experimental evolution; growth rate hypothesis; r/K strategies; stoichiometry