Monday, June 2, 2008

SMBE '08

I'll be attending the Society for Molecular Biology and Evolution's annual meeting in Barcelona, Spain. (Is anyone else attending?) At the meeting, I'll be presenting results from a sequencing study I did of bacteriophage populations that were evolved under sexual or asexual conditions. Surprisingly the asexual populations were more genetically diverse than sexual ones.

The study was motivated by the idea that sex generates genetic diversity.

The idea that sex functions to provide variation for natural selection to act upon was first advocated by August Weismann and it has dominated much discussion on the evolution of sex and recombination since then.” A. Burt, Evolution, 2000

Sex in phages is a function of the multiplicity of infection (MOI). When multiple phi6 phages infect the same host cell, they can reassort segments of their genomes.

Previously Dr. Paul Turner evolved populations of phi6 at either high or low MOI for 300 generations. The results were published in Genetics.
I hypothesized that sex increased diversity among phages. To test this hypothesis, I sequenced parts of the phi6 genome for ten clones of each of the six evolved populations. The results indicated that the asexual populations had more genetic diversity than the sexual populations.
I interpreted these results as indicative of the purifying selection of sex. Asexual populations are prone to clonal interference, i.e. multiple beneficial alleles compete with each other, but cannot be integrated into the same genotype as sex permits. So, the genetic diversity of the asexual populations remain high, while the sexual populations quickly fix the best available genotype.

The results will be submitted for publication later this year with my co-authors Siobain Duffy, Aashish Jethra, Kara O'Keefe, Scott Edwards, and Paul Turner.


  1. I see you hypothesized sex would increase diversity, but did you expect it to?

  2. Actually I was kind of agnostic about the issue. At the time, I could think of strong arguments for either case. However, I was surprised when the data showed that asexuals were so clearly more diverse.

  3. John,

    Cool findings, consistent with the dynamics reported by Tim Cooper in PLOS in bacteria.

    Glad that you reported these results here, and so I will be sure to add this blog to the blogroll at, a blog network for classes and collaborations in our subject.

    Hope you won't mind the traffic, and hope I can get you to participate!

    Vaughn Cooper

  4. Very cool site, Vaughn. Nice way to engage your students in microbial population biology. I'd be glad to participate in any way I can.