Evolutionary Genetics of Borrelia burgdorferi sensu lato
Daniel Dykhuizen and Dustin Brisson
from: Borrelia: Molecular Biology, Host Interaction and Pathogenesis (Edited by: D. Scott Samuels and Justin D. Radolf). Caister Academic Press, U.K. (2010)
Evolution can inform our understanding of the biology of Borrelia. Four forces propel evolutionary change: mutation, genetic drift, migration and natural selection. Although these microevolutionary forces act primarily within populations, the same forces create macroevolutionary divergence of species. The prevailing data suggest that Borrelia burgdorferi sensu lato was once a wide-ranging species in the Northern Hemisphere that rapidly separated into the species present today. The limited neutral divergence within species suggests that the long-term effective population size is small. The combined observations that Borrelia was once a very wide-ranging species and that the current effective population sizes of the species are very small suggests that Borrelia populations can expand rapidly when conditions are favorable and shrink rapidly when conditions are unfavorable. Divergence among and within genospecies has progressed primarily by mutation, as horizontal gene transfers are rare; so rare that most observed recombinants seen in nature are likely to have been selected to maintain genetic diversity. Recent migration, as well as range expansions and contractions, have resulted in overlapping patchy distributions of genospecies across the Northern Hemisphere. Most likely, infected birds are responsible for long distance migration, while infected mammals are important in range expansion and migration between local populations. Natural selection, especially that promoting host specificity, continues to shape the geographic distribution as well as the genetic diversity within and between species read more ...