title: Chemical warfare and survival strategies in bacterial range expansions.
abstract: Dispersal of species is a fundamental ecological process in the evolution and maintenance of biodiversity. Limited control over ecological parameters has hindered progress in understanding of what enables species to colonize new areas, as well as the importance of interspecies interactions. Such control is necessary to construct reliable mathematical models of ecosystems. In our work, we studied dispersal in the context of bacterial range expansions and identified the major determinants of species coexistence for a bacterial model system of three Escherichia coli strains (toxin-producing, sensitive and resistant). Genetic engineering allowed us to tune strain growth rates and to design different ecological scenarios (cyclic and hierarchical). We found that coexistence of all strains depended on three strongly interdependent factors: composition of inoculum, relative strain growth rates and effective toxin range. Robust agreement between our experiments and a thoroughly calibrated computational model enabled us to extrapolate these intricate interdependencies in terms of phenomenological biodiversity laws. Our mathematical analysis also suggested that cyclic dominance between strains is not a prerequisite for coexistence in competitive range expansions. Instead, robust three-strain coexistence required a balance between growth rates and either a reduced initial ratio of the toxin-producing strain, or a sufficiently short toxin range.
authors.affiliation: Arnold Sommerfeld Center for Theoretical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, , Theresienstraße 37, Munich 80333, Germany.
authors.forename: Markus F
authors.initials: MF
authors.lastname: Weber
authors.forename: Gabriele
authors.initials: G
authors.lastname: Poxleitner
authors.forename: Elke
authors.initials: E
authors.lastname: Hebisch
authors.forename: Erwin
authors.initials: E
authors.lastname: Frey
authors.forename: Madeleine
authors.initials: M
authors.lastname: Opitz
mesh_terms: D044822:Biodiversity; D005075:Biological Evolution; D017753:Ecosystem; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005818:Genetic Engineering; D008954:Models, Biological
keywords: Escherichia coli; bacterial model systems; maintenance of biodiversity; microbial ecology; range expansions; species coexistence