TABLE 2

The effects of stabilizing selection on the distribution of fixed mutational effects

No. of charactersAverage scaled fixed effectAverage scaled fixed effect magnitude% negative effectsa
20.500.7026.4
50.290.6037.0

Under stabilizing selection, adaptation began the magnitude of two random mutations away from the optimum for each character and stopped once the phenotype traveled 90% of the distance to the optimum. The effective and census population sizes were both 2 × 105. One thousand replicates of the adaptive process occurred for each value. Random mutation was bilaterally symmetric and exponentially distributed.

  • a A character began adaptation to one side of the optimum, and the direction of effects is standardized relative to this initial positioning. Negative effects correspond to mutations that fixed in the opposite direction of the optimum relative to the initial positioning of a character.