FIG 4.

Evolutionary model for reference marine microbes (RMM) and SAR11 populations. RMM evolution is characterized by “hard” selective sweeps that reduce genomic diversity, and only a single adaptive lineage arises from the population. However, SAR11 evolution is characterized by “soft” sweeps, where multiple beneficial mutations contribute to an adaptive substitution, which are dispersed by the population, contributing to an increase in genetic diversity. (A) Relative abundances of the populations (y axis) and evolution over time (x axis). (B) Dynamics of different evolutionary parameters over time, where each vertical dotted line differentiates different diversification events in RMM, while in SAR11 populations, the same structure is maintained over time. (C) Recruitment plot showing intrapopulation sequence diversity. The red dashed line indicates the species threshold (95%). Different colors indicate different populations.