variance components

Pérez-Figueroa A, Caballero A, García-Dorado A & López-Fanjul C 2009 The action of purifying selection, mutation and drift on fitness epistatic systems. Genetics 183:299-313.

  • our aim was to describe and analyze drift-induced changes in the components of the genetic variance of fitness
  • where neutral predictions will be reliable only during extreme and brief bottlenecks
  • for moderate bottleneck sizes or long-term inbreeding, it becomes necessary to consider the concurrent effects of natural selection both on the standing variation and on that arisen by new mutation
  • for nonepistatic models, the genetic properties of the trait can be theoretically inferred from the pertinent mutational parameters and effective population sizes by assuming a balance between mutation, selection, and drift
  • this can be numerically achieved using diffusion theory, and reliable approximations can be easily calculated by analytical methods (García-Dorado 2007)
  • the epistatic component of variance VI is independent of the degree of dominance of the loci involved
  • in some cases, fitness showed a slight fitness rebound after an initial inbreeding depression
  • this was appreciable only for models I and II with N = 10 and cannot be accounted for by García-Dorado's approach
  • for N ≥ 10, the MSD decline (both predicted and simulated) was much smaller than that obtained in the D scenario
  • an outcome that must be ascribed to natural selection (partially) purging recessive deleterious alleles
  • for N = 2, however, selection was quite inefficient, implying early fitness declines almost as large as those obtained in the D scenario and substantial later declines from new deleterious mutation
  • in practice, the efficiency of natural selection to promote new favorable epistatic combinations was not enhanced by bottlenecking
  • selection prevented between-line differentiation irrespective of the presence of epistasis
  • the antagonistic epistasis systems studied did not qualitatively modify the evolutionary pattern for synergistic epistasis described above
  • in spite of the two-peak adaptive surface produced by the former system
  • the deleterious properties of spontaneous mutations primarily imply purifying selection
  • nonadditive gene action, including epistasis, does not usually increase evolutionary rates, even for systems generating two-peak adaptive surfaces