Variation of three morphological traits (thorax length, wing length and sternopleural bristle number) was examined in Drosophila melanogaster reared on a medium with low yeast content and on a standard medium using the isofemale line analysis and offspring--parent regression. The aim was to test whether these experimental approaches give different patterns of changes in genetic variability estimates when stressful and nonstressful environments are compared. Heritabilities and genetic and phenotypic variances were generally higher in the isofemale line design than in the offspring--parent regression design under both standard and poor nutritional conditions. For each trait, the response of heritability to stress was similar in both designs: wing length exhibited lower heritability under poor nutrition, whereas heritabilities of thorax length and sternopleural bristle number did not differ between nutritional regimes. Statistically significant differences in the genetic variances and the environmental variances between stressful and nonstressful environments were recorded only in isofemale lines: the genetic variance of thorax length and the environmental variances of thorax length and wing length were higher under poor nutrition. The results are compared to literature data and possible reasons of increased genetic variability estimates in isofemale lines are briefly discussed.
