Modeling selective pressures on phytoplankton in the global ocean

Area of Science:

• Marine microbiology
• Oceanography
• Evolutionary biology

Background:

• Culture-independent methods reveal marine microbial diversity.
• Understanding marine microbe ecology and evolution is challenging due to complex shaping forces.
• Synechococcus and Prochlorococcus cyanobacteria exhibit different nitrogen use abilities.

Purpose of the Study:

• To model selective pressures on nitrogen use abilities in marine picophytoplankton.
• To determine ocean regions where losing nitrate use is disadvantageous.
• To understand the evolution of nitrogen use traits in Synechococcus and Prochlorococcus.

Main Methods:

• Incorporation of physical, biogeochemical, ecological, and mutational forces into a global ocean model.
• Simulation of mutations for loss of nitrogen use abilities in modeled picophytoplankton.
• Analysis of selective disadvantage across different ocean regions and seasonal dynamics.

Main Results:

• The selective disadvantage of losing nitrate use is smallest in tropical regions where Prochlorococcus are abundant.
• Higher latitudes, where Synechococcus are abundant, show a larger selective disadvantage for nitrate loss.
• Model ecotypes with Prochlorococcus-like seasonal dynamics are less disadvantaged by nitrate loss than Synechococcus-like ecotypes.

Conclusions:

• Model predictions align with the observed distribution of nitrate use ability in marine picocyanobacteria.
• The study provides insights into the interplay between ocean processes and selective pressures on marine microbes.
• This approach facilitates testing hypotheses about genetic variation drivers in marine microbial evolution.