Evolutionary Genetic Species Detected in Prokaryotes by Applying the K/θ Ratio to DNA Sequences

Abstract

Previous papers in this series described the "evolutionary genetic species concept" which is based on population genetic theory and should be applicable to any organism. Also described was a species criterion, the K/{theta} ratio, that delimits independently evolving evolutionary species based on single-gene sequences, and its application to sexual and asexual eukaryotes was illustrated. Here, we show how the evolutionary genetic species concept and the K/{theta} ratio can be applied to bacteria, using the sequences from some genes of the core genome that are rarely, if ever, transferred horizontally between different species. This completes the demonstration that K/{theta} is a general method for species delimitation, applicable to all organisms. Also, it adds to the evidence that bacteria have species in the most general sense, even though they have the ability to exchange genes across species boundaries. Finally, we show that a published critique of the use of K/{theta} [≥] 4 as a criterion for independently evolving species rests on two errors in the application of population/evolutionary genetic theory.