Gounand, I., T. Daufresne, D. Gravel, C. Bouvier, T. Bouvier, M. Combe, C. Gougat-Barbera, F. Poly, C. Torres-Barcelo, Mouquet, N. (2018).

Proceedings of the Royal Society B-Biological Sciences 283, doi:10.1098/rspb.2016.2272

Key message : 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 (mmax) from a single bacterium ancestor to test the relationship among mmax, competitive ability for nutrients and cell size, while controlling for evolutionary history. We found a strong positive correlation between mmax and competitive ability for phosphorus, associated with a trade-off between mmax and cell size: strains selected for high mmax were smaller and better competitors for phosphorus. Our results strongly support the SH, while the trade-offs expected under GRH were not apparent.. Our study stresses that physiological links between these traits tightly shape the evolution of competitive strategies.

Relationship between maximum growth rate mmax on low-P medium and competitive ability for Phosphorus CP (a), or relative cell size (b), of evolved strains. Values were rank transformed to correspond to the non-parametric test we used. Competitive ability was approximated with maximum optical density obtained during 70 h of bacterial growth. Relative cell size was approximated with the geometric mean of the FSC-H parameter distribution of 50 000 events by population measured with flow cytometry. Symbols represent averages of five measurements per strain. TV units are in microlitres.

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OTHER TOPICS: Aesthetics of Biodiversity, Biodiversity & Ecosystem Functioning, Biogeography, Macroecology & Ecophylogenetics, Experimental Evolution, Functional Biogeography, Functional Rarity, Metacommunities, Metaecosystems, Reviews and Synthesis, Trophic Biogeography & Metaweb