Understanding the conditions that allow speciation to occur is difficult because most research has focused on either long-lived organisms or asexual microorganisms. We propagated bacteriophage λ, a virus with rapid generations and frequent recombination, on two Escherichia coli host genotypes that expressed either the LamB or OmpF receptor. When supplied with either single host (allopatry), λ improved its binding to the available receptor while losing its ability to use the alternative. When evolving on both hosts together (sympatry), the viruses split into two lineages with divergent receptor preferences. Although the level of divergence varied among replicates, some lineages evolved reproductive isolation via genetic incompatibilities. This outcome indicates that, under suitable conditions, allopatric and sympatric speciation can occur with similar ease.

Meyer Science 2016 Fig 1AData collected for results shown in figure 1a, see notes within the file and the manuscript for further guidance.Meyer Science 2016 Fig 1BData collected for results shown in figure 1b, see notes within the file and the manuscript for further guidance.Meyer Science 2016 Fig 2Data collected for results shown in figure 2, see notes within the file and the manuscript for further guidance.Meyer Science 2016 Fig 3Data collected for results shown in figure 3, see notes within the file and the manuscript for further guidance.Meyer Science 2016 Fig 4CData collected for results shown in figure 4c, see notes within the file and the manuscript for further guidance.Meyer Science 2016 Fig S1Data collected for results shown in figure S1, see notes within the file and the manuscript for further guidance.