Mutation as a Lens on Natural Selection in C. elegans

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Charles F. Baer, Ph.D.
Department of Biology
University of Florida Genetics Institute

Understanding the relative contributions of the different evolutionary forces to phenotypic evolution is a central mission of population and quantitative genetics.  As a starting point, it is important to isolate the contributions of mutation from the other forces, because mutation can never be "turned off".  A Mutation Accumulation (MA) experiment provides a way to quantify the cumulative effects of mutation in the (near) absence of natural selection.  Then, comparison of the properties of genetic variation introduced by mutation to those of the standing genetic variation within and/or between populations provides insight into what natural selection does or does not want.  

We use data from a set of C. elegans MA lines to address two fundamental questions in evolution.  First, we quantify the amount of mutational input into the mutational process itself.  We find that the genome-wide mutation rate evolves significantly upward over a few hundred generations of relaxed natural selection.  Second, we compare two independent measures of selection acting on new spontaneous mutations, one of which is conceptually airtight but of limited utility, the other of which is conceptually suspect but of broad utility (and widely applied).  Happily (or coincidentally), the two measures agree with within a factor of two.  We further show that new spontaneous mutations interact synergistically, potentially explaining why we have not Died 100 Times Over.  Finally, we show that the base-substitution spectrum of experimentally accumulated mutations differs significantly from the spectrum of standing rare variants.  That discrepancy means either (a) that natural selection skews the spectrum, or (b) mutations accumulated in the lab do not faithfully reflect the natural spectrum.  We increasingly suspect the latter.

Host: Soojin Yi, Ph.D.


  • Workflow Status:Published
  • Created By:Jasmine Martin
  • Created:04/12/2019
  • Modified By:Jasmine Martin
  • Modified:04/12/2019