Developmental stability opf Drosophila melanogaster under artificial and natural selection in constant and fluctuating environments.

Populations of Drosophila melanogaster in constant 25 degrees and fluctuating 20/29 degrees environments showed increases in developmental stability, indicated by decreases in bilateral asymmetry of sterno-pleural chaeta number. In both environments, rates of decrease in asymmetry were greater under natural selection (control lines) than under artificial stabilizing selection. Overall mean asymmetry was greater in the fluctuating environment.--There was no evidence that decreased asymmetry was due to heterozygosity, and the decline in asymmetry was not explained by the decline in chaeta number in the lines under natural selection. However, the decline was consistent with changes in total phenotypic variance and environmental variance.--The divergence between lines after 39 generations of selection was seen in differences in asymmetry and also in the genotype-environment interaction expressed in cross-culturing experiments.