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Contrasting dynamics of a mutator allele in asexual populations of differing size

Yevgeniy Raynes1, Matthew R Gazzara, Paul D Sniegowski

  • 1Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA. yraynes@sas.upenn.edu

Evolution; International Journal of Organic Evolution
|July 5, 2012
PubMed

Insights

Mutator hitchhiking, where increased mutation rates benefit asexual populations, is inhibited in very large populations. This occurs due to clonal interference and the mutator allele

Area of Science:

  • Evolutionary Biology
  • Microbial Genetics

Background:

  • Mutator strains, characterized by elevated mutation rates, can increase the supply of beneficial mutations in asexual populations.
  • The hitchhiking of mutators is typically favored when their beneficial mutation supply rate exceeds that of wild-type strains.

Purpose of the Study:

  • To investigate the impact of total population size on the dynamics of mutator strains in asexual populations of Saccharomyces cerevisiae.
  • To understand the conditions under which mutator hitchhiking may be inhibited in natural populations.

Main Methods:

  • Experimental evolution using Saccharomyces cerevisiae populations of varying sizes.
  • Monitoring the frequency and fixation of mutator strains over time.

Main Results:

  • Mutators hitchhiked to fixation rapidly in smaller populations.
  • Fixation time for mutators increased with population size, consistent with clonal interference.
  • In very large populations, mutators were outcompeted by wild-type strains, a reversal of expected dynamics.

Conclusions:

  • Clonal interference, mutator fitness costs, and infrequent large-effect beneficial mutations interact to inhibit mutator hitchhiking in large populations.
  • These findings identify specific conditions that can prevent the accumulation of higher genomic mutation rates in natural asexual populations, contrary to some theoretical predictions.

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