Research Article

Repeatability and Contingency in the Evolution of a Key Innovation in Phage Lambda

See allHide authors and affiliations

Science  27 Jan 2012:
Vol. 335, Issue 6067, pp. 428-432
DOI: 10.1126/science.1214449

You are currently viewing the editor's summary.

View Full Text

Log in to view the full text

Log in through your institution

Log in through your institution

Natural Selection Caught in the Act

Understanding how new functions evolve has been of long-standing interest. However, the number of mutations needed to evolve a key innovation is rarely known, or whether other sets of mutations would also suffice, whether the intermediate steps are driven by natural selection, or how contingent the outcome is on steps along the way. Meyer et al. (p. 428; see the Perspective by Thompson) answer these questions for a case in which phage lambda evolved the ability to infect its host Escherichia coli through a novel receptor. This shift required four mutations, which accumulated under natural selection in concert with coevolution of the host. However, when Tenaillon et al. (p. 457) exposed 115 lines of E. coli to high temperature and sequenced them, adaptation occurred through many different genetic paths, showing parallelism at the level of genes and interacting protein complexes, but only rarely at the nucleotide level. Thus, epistasis—nonadditive genetic interaction—is likely to play an important part in the process of adaptation to this environment.