compensatory evolution

Denver DR, Howe DK, Wilhelm LJ, Palmer CA, Anderson JL, Stein KC, Phillips PC & Estes S 2010 Selective sweeps and parallel mutation in the adaptive recovery from deleterious mutation in Caenorhabditis elegans. Genome Res 20:1663-1671.

  • DNA sequencing analysis of bacteriophage ΦX174 lines that had recovered from previously accumulated deleterious mutations revealed that ~30% of the beneficial mutations responsible for fitness recovery were back mutations (direct mutational reversals)
  • the remaining ~70% were compensatory mutations at other sites in the phage genome
  • ~95% of the beneficial mutations detected in Salmonella typhimurium lab populations recovering from the deleterious effects of antibiotic resistance were compensatory in nature rather than reversions
  • the much larger genome sizes (>100 Mb for C. elegans versus ~5.3 kb for ΦX174) of multicellular species have thus far precluded analyses of genomic divergence patterns associated with adaptive recovery from deleterious mutation similar to those carried out in prokaryotic systems
  • none of the recovery response is attributable to detectable reversion mutations
  • no cases of putative intragenic compensatory mutations were identified
  • intergenic compensatory mutations likely drive all of the change that we observe
  • this might be a common avenue for genetic change within complex multicellular organisms
  • two identical fixed mutations were detected in R12A and R12C that most likely arose and fixed in these two recovery lineages in an independent, parallel fashion
  • parallel mutation has previously been observed in similar experimental evolution studies in prokaryotes
  • the observation of two sites fixing the exact same mutation type in independent recovery lines suggests that these mutations might have beneficial effects that were directly acted upon by natural selection
  • the observation of parallel mutation in the recovery lines might reflect a limited number of beneficial mutations available as potential substrates for adaptive recovery from MA12 mutations (Orr 2005)
  • both parallel mutations, however, occurred in genomic regions that are not predicted to encode functional protein products
  • any positive effects would be mediated through regulatory or DNA structural effects