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Ecological speciation of bacteriophage lambda in allopatry and sympatry

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Science  09 Dec 2016:
Vol. 354, Issue 6317, pp. 1301-1304
DOI: 10.1126/science.aai8446

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A laboratory model of viral speciation

New species arise through the evolution of barriers to reproduction. This process is well understood where the emerging species are spatially isolated from one another. But the process of sympatric speciation—where the diverging species co-occur—is more enigmatic. Bacterial viruses make good models for addressing such questions because of their rapid generation times. Meyer et al. took bacteriophage λ and grew it on a mix of two strains of Escherichia coli. The virus duly split its host preferences into lineages with differing affinity for their respective E. coli hosts. In some experiments, the phages diverged to the extent that they became reproductively restricted to one strain of E. coli, even when the other was present.

Science, this issue p. 1301

Abstract

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), phage 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.

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