Selection for ethanol tolerance in two populations of Drosophila melanogaster segregating alcohol dehydrogenase allozymes.

Selection for ethanol tolerance was equally successful in two populations of D. melanogaster in both of which the frequency of AdhF was 0.5 at the start of the experiment. Increased tolerance to ethanol was not invariably associated with increased frequencies of AdhF. In one population alcohol dehydrogenase (ADH) activity was significantly higher in three of the four selected sublines compared with their controls but there was no difference in activity between the selected and control sublines in the second population. The level of ADH activity in the control and selected lines was significantly correlated with the frequency of AdhF, but not with ethanol tolerance. These results show that adaptation to environmental alcohols in populations of D. melanogaster can be independent of the ADH system.