Bacteria are different: Observations, interpretations, speculations, and opinions about the mechanisms of adaptive evolution in prokaryotes

Abstract

To some extent, the genetical theory of adaptive evolution in bacteria is a simple extension of that developed for sexually reproducing eukaryotes. In other, fundamental, ways the process of adaptive evolution in bacteria is quantitatively and qualitatively different from that of organisms for which recombination in an integral part of the reproductive process. In this speculative and opinionated perspective, we explore these differences. In particular, we consider (1) how, as a consequence of the low rates of recombiation, "ordinary" chromosomal gene evolution in bacteria is different from that in organisms where recombination is frequent, and (2) the fundamental role of the horizontal transmission of genes and accessory genetic elements as sources of variation in bacteria. We conclude with specualtions about the evolution of accessory elements and their role in the adaptive evolution of bacteria.