title: Recurrent evolution of host and vector association in bacteria of the Borrelia burgdorferi sensu lato species complex.
abstract: The Borrelia burgdorferi sensu lato (s.l.) species complex consists of tick-transmitted bacteria and currently comprises approximately 20 named and proposed genospecies some of which are known to cause Lyme Borreliosis. Species have been defined via genetic distances and ecological niches they occupy. Understanding the evolutionary relationship of species of the complex is fundamental to explaining patterns of speciation. This in turn forms a crucial basis to frame testable hypotheses concerning the underlying processes including host and vector adaptations.
  
  
  
  Illumina Technology was used to obtain genome-wide sequence data for 93 strains of 14 named genospecies of the B. burgdorferi species complex and genomic data already published for 18 additional strain (including one new species) was added. Phylogenetic reconstruction based on 114 orthologous single copy genes shows that the genospecies represent clearly distinguishable taxa with recent and still ongoing speciation events apparent in Europe and Asia. The position of Borrelia species in the phylogeny is consistent with host associations constituting a major driver for speciation. Interestingly, the data also demonstrate that vector associations are an additional driver for diversification in this tick-borne species complex. This is particularly obvious in B. bavariensis, a rodent adapted species that has diverged from the bird-associated B. garinii most likely in Asia. It now consists of two populations one of which most probably invaded Europe following adaptation to a new vector (Ixodes ricinus) and currently expands its distribution range.
  
  
  
  The results imply that genotypes/species with novel properties regarding host or vector associations have evolved recurrently during the history of the species complex and may emerge at any time. We suggest that the finding of vector associations as a driver for diversification may be a general pattern for tick-borne pathogens. The core genome analysis presented here provides an important source for investigations of the underlying mechanisms of speciation in tick-borne pathogens.
authors.affiliation: Faculty of Biology, Division of Evolutionary Biology, Ludwig Maximilians University of Munich, Grosshaderner Strasse 2, 82152, Planegg-Martinsried, Germany. nbecker@bio.lmu.de.
authors.forename: Noémie S
authors.initials: NS
authors.lastname: Becker
authors.affiliation: National Reference Centre for Borrelia at the Bavarian Health and Food Safety Authority, Veterinärstr. 2, 85764, Oberschleissheim, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Margos
authors.affiliation: Gene Center, Laboratory for Functional Genome Analysis, Ludwig Maximilians University of Munich, Feodor-Lynen-Strasse 25, 81377, Munich, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Blum
authors.affiliation: Gene Center, Laboratory for Functional Genome Analysis, Ludwig Maximilians University of Munich, Feodor-Lynen-Strasse 25, 81377, Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Krebs
authors.affiliation: Gene Center, Laboratory for Functional Genome Analysis, Ludwig Maximilians University of Munich, Feodor-Lynen-Strasse 25, 81377, Munich, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Graf
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Lane
authors.affiliation: Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210, Cuernavaca, Morelos, Mexico.
authors.forename: Santiago
authors.initials: S
authors.lastname: Castillo-Ramírez
authors.affiliation: National Reference Centre for Borrelia at the Bavarian Health and Food Safety Authority, Veterinärstr. 2, 85764, Oberschleissheim, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Sing
authors.affiliation: National Reference Centre for Borrelia at the Bavarian Health and Food Safety Authority, Veterinärstr. 2, 85764, Oberschleissheim, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Fingerle
mesh_terms: D000818:Animals; D005075:Biological Evolution; D015748:Borrelia burgdorferi Group / Q000145:classification* / Q000235:genetics*; D056426:Genetic Loci; D014644:Genetic Variation; D005838:Genotype; D054884:Host-Pathogen Interactions; D007303:Insect Vectors / Q000382:microbiology*; D008193:Lyme Disease / Q000382:microbiology / Q000635:transmission; D009154:Mutation; D010802:Phylogeny; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA
keywords: Borrelia burgdorferi sensu lato; Evolution; Host association; Lyme disease; Population genomics; Vector adaptation