Changes in Population Age-Structure Obscure the Temperature-Size Rule in Marine Cyanobacteria.

Antonio S Palacio,Ángel López-Urrutia,Francisca C García,Laurence Garczarek,Laura Alonso-Sáez,Ana María Cabello,Xosé Anxelu G Morán,Abbrar Labban

doi:10.3389/fmicb.2020.02059

Abstract

The temperature-size Rule (TSR) states that there is a negative relationship between ambient temperature and body size. This rule has been independently evaluated for different phases of the life cycle in multicellular eukaryotes, but mostly for the average population in unicellular organisms. We acclimated two model marine cyanobacterial strains (Prochlorococcus marinus MIT9301 and Synechococcus sp. RS9907) to a gradient of temperatures and measured the changes in population age-structure and cell size along their division cycle. Both strains displayed temperature-dependent diel changes in cell size, and as a result, the relationship between temperature and average cell size varied along the day. We computed the mean cell size of new-born cells in order to test the prediction of the TSR on a single-growth stage. Our work reconciles previous inconsistent results when testing the TSR on unicellular organisms, and shows that when a single-growth stage is considered the predicted negative response to temperature is revealed.

Highlights

Organism size is one of the most fundamental functional traits in ecology affecting all levels of biological organization from individual fitness to ecosystem processes (Brown et al, 2004; Kingsolver and Huey, 2008)
We studied the effect of temperature on their growth rate, cell division cycle and the corresponding relationships between temperature and cell size, taking into account differences produced by changes in the age-structure of the populations
One of the main conclusions of this work is that testing the Temperature size rule” (TSR) in unicellular organisms is more challenging than previously considered in earlier studies

Summary

Introduction

Organism size is one of the most fundamental functional traits in ecology affecting all levels of biological organization from individual fitness to ecosystem processes (Brown et al, 2004; Kingsolver and Huey, 2008). Organism size can respond to different environmental conditions, with temperature being one of the main regulating factors (Kingsolver and Huey, 2008). An inverse correlation between body size and ambient temperature exists in a wide range of organisms, including bacteria, protist, plants and animals (Forster et al, 2012). The “Temperature size rule” (TSR) (Atkinson, 1994) considers this inverse correlation between temperature and body size as the result of phenotypic plasticity. Several studies have found support for the TSR analyzing different types of organisms. The relationship between temperature and body size has seldom been explored

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Results

Conclusion