Genetic and environmental factors in the resistance of Drosophila subobscura adults to high temperature shock : 2. Modification of heat resistance by indirect selection.

We have carried out two equivalent selection experiments to increase and decrease heat shock resistance of Drosophila subobscura adults, using an indirect selection method that avoids excessive consanguinity. Heat shock was 33±0.5 °C at saturation humidity. Control lines showed a rapid change of the physiological trait as a consequence of laboratory culture conditions, expressed as a decrease both in heat shock resistance and in the initial population variability for heat shock resistance. Thus, this reduction of variability seems to consist in the loss of those combinations of genes that confer high resistance to heat shock. After eight generations of selection, the selected lines were differentiated from their respective control lines, and the selection response obtained was similar in "resistant" and "sensitive" lines. Differences in survival of progeny of reciprocal crosses between selected lines suggest that inheritance of heat resistance may depend in part on the origin of egg cytoplasm.