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

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.02059

DOI=10.3389/fmicb.2020.02059

ISSN=1664-302X

ABSTRACT=<p>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 (<italic>Prochlorococcus marinus</italic> MIT9301 and <italic>Synechococcus sp.</italic> 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.</p>