Lateral gene transfer is of fundamental importance to the evolution of prokaryote genomes and has important practical consequences, as evidenced by the rapid dissemination of antibiotic resistance and virulence determinants. Relatively little effort has so far been devoted to explicitly quantifying the rate at which accessory genes are taken up and lost, but it is possible that the combined rate of lateral gene transfer and gene loss is higher than that of point mutation. What evolutionary forces underlie the rate of lateral gene transfer are not well understood. We here use theory developed to explain the evolution of mutation rates to address this question and explore its consequences for the study of prokaryote evolution.

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