A Model for the Effect of Homologous Recombination on Microbial Diversification

The effect of homologous recombination (HR) on the evolution of microbial genomes remains contentious as competing hypotheses seek to explain the evolutionary dynamics of microbial species. Evidence for HR between microbial genomes is widespread, and this process has been proposed to act as a cohesive force that can constrain the diversification of microbial lineages. We seek to characterize the evolutionary dynamics of sympatric populations to explore the impact of HR on microbial speciation. We describe a simple equation for quantifying the cohesive effect of HR on microbial populations as a function of their nucleotide divergence, μ/ρ=πg10(-20 πg). The model was verified using a forward-time microbial population simulator that can explore the evolutionary dynamics of sympatric populations in nonoverlapping niche space. The model was also evaluated using multilocus sequence data from a range of microbial species, providing criteria for dividing them into either cohesively recombining or clonally diverging lineages. We conclude that models of microbial diversification that appear contradictory can be explained in a unified manner as the natural and predictable consequence of variation in a small number of population parameters.