A Simulation Study of Truncation Selection for a Quantitative Trait Opposed by Natural Selection

Abstract

A quantitative character controlled at one locus with two alleles was submitted to artificial (mass) selection and to three modes of opposing natural selection (directional selection, overdominance and underdominance) in a large random-mating population. The selection response and the limits of the selective process were studied by deterministic simulation. The lifetime of the process was generally between 20 and 100 generations and did not appear to depend on the mode of natural selection. However, depending on the values of the parameters (initial gene frequency, selection intensity, ratio of the effect of the gene to the environmental standard deviation, fitness values) the following outcomes of selection were observed: fixation of the allele favored by artificial selection, stable nontrivial equilibrium, unstable equilibrium and loss of the allele favored by artificial selection. Finally, the results of the simulation were compared to the results of selection experiments.

Accumulation of lethals in highly selected lines of Drosophila melanogaster

“…The increasing opposition of natural selection often causes a cessation of response in artificial selection experiments. In spite of genetic variation for the selected trait, a limit to selection is reached which can be characterised by an unstable equilibrium between these two forces (A1-Murrani 1974; Verghese 1974;Minvielle 1980;Nicholas and Robertson 1980).…”