Presentation Detail

Experimental Evolution

Burmeister, Alita [1], Meyer, Justin [2], Lenski, Richard [3].

Coevolution Facilitates the Evolution of a Novel Function in Phage Lambda by Altering the Fitness Landscape.

The evolution of novelty, whereby lineages evolve qualitatively new functions, is rare but important. Such evolutionary innovations are rare because they typically require multiple evolutionary steps, some of which may not be adaptive. Despite their rarity, a recent study caught this process in action, when a virus, bacteriophage Lambda, repeatedly evolved the ability to exploit a new receptor (host outer-membrane protein OmpF) during the course of a laboratory experiment. The innovation required four specific mutations in the J gene that encodes the virus's host-recognition protein. We hypothesized that the virus evolved this seemingly unlikely combination of mutations as a coevolutionary response to its host, Escherichia coli, evolving resistance. During the experiment, an E. coli mutation had first caused altered presentation of its native receptor (another outer-membrane protein, LamB), which likely rendered the ancestral Lambda J protein maladapted for host recognition. To test whether this host resistance favored the new J variants, we isolated six Lambda genotypes that had acquired various subsets of the four J mutations, but which did not allow the transition to use OmpF. We compared the relative fitness of each genotype against the ancestral Lambda when competing for either sensitive or resistant host cells. Consistent with our hypothesis, all six intermediate phage genotypes had increased fitness on the resistant host. This study shows that coevolution can promote the evolution of novelty by altering the structure of the fitness landscape.

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Description of the work written for a general audience

1 - Michigan State University, 567 Wilson Road, 6176, East Lansing, MI, 48824, USA
2 - Harvard Medical School, 536 Warren Alpert, Boston, MA, 02115, USA
3 - Michigan State University, 567 Wilson Road, 6177, East Lansing, MI, 48824, USA

Keywords:
adaptive landscape
Coevolution
Experimental Evolution
E. coli
bacteriophage
novelty
host-parasite
predator-prey.

Presentation Type: Regular Oral Presentation
Session: 56
Location: Rendezvous B/Snowbird Center
Date: Sunday, June 23rd, 2013
Time: 9:45 AM
Number: 56006
Abstract ID:240
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation