Evolution of phytoplankton cell size in a variable environment

Ariane Verdy (June 28, 2011)

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The size of phytoplankton cells determines their competitive ability, sinking rate, and potential to export carbon to the deep ocean. Observations suggest that small phytoplankton species dominate the equatorial and subtropical oceans while larger species are more abundant in subpolar regions. To understand this pattern, we have developed an allometric model for the evolution of phytoplankton cell size. The model shows that increasing body size can be a successful adaptation, even in the absence of temporal variability or predation. The evolutionarily stable strategy is set by the allometric relationships for nutrient uptake kinetics and by metabolism. In a simple chemostat model, fluctuations in resource supply increase the optimal cell size. I will discuss the organization of phytoplankton communities along a latitudinal gradient in nutrient supply, sea surface temperature, and insolation.