Stabilizing and disruptive selection on a mutant character in Drosophila. IV. Selection on sensitivity to temperature.

Individual selection on temperature sensitivity was applied to the relative length of the 4th vein of the mutant ci(D-G) in four selection lines according to different selection schemes indicated in Figure 1. These selection systems include, besides the selection on temperature, disruptive selection. In all lines the disruptive component causes an increase of the phenotypic variance, but there are large differences in its composition. The selection changed temperature sensitivity in the expected direction in all lines. In one line (C-D(-)) however, the change in temperature sensitivity and the increase in variance were only small because the disruptive component and the canalizing component of the selection scheme restricted each others' effect. The results are discussed in relation to earlier results obtained by disruptive selection at one temperature.