Diverse strategies link growth rate and competitive ability in phytoplankton responses to changes in CO2 levels

Aquatic microbial primary producers exist in genetically variable populations, but are often studied as single lineages. However, the properties of lineages grown alone often fail to predict the composition of microbial assemblages. We demonstrate that different lineages of a marine picoplankter have unique growth strategies, and that they modulate their lineage growth rate in the presence of other lineages. This explains why growth rates of lineages in isolation do not reliably predict the lineage composition of assemblages. The diversity of growth strategies observed are consistent with lineage-specific energy-allocation that depends on social milieu. Since lineage growth is only one of many traits determining fitness in natural assemblages, we propose that in all but the poorest quality environments where allocating maximum energy to growth is the only viable strategy, we should expect intraspecific variation in growth strategies, with more strategies possible in ameliorated environments, such as high CO 2 for many marine picoplankton. This emphasizes the importance of understanding and accounting for basic organismal biology in our models of aquatic primary producers. Data archiving Should this manuscript be accepted, data will be archived at Pangea, and the DOI be included at the end of the article