Ethanol tolerances of Drosophila melanogaster populations selected on different concentrations of ethanol supplemented media.

Eight recently collected Australasian populations of D. melanogaster were each divided into eight selection lines. Two of these lines from each population were maintained on one of four types of selection media: standard food supplemented with 0%, 3%, 6% and 9% ethanol. After 30 generations the selection lines were tested for tolerance to 9% ethanol medium and after another 20 generations adults were tested for tolerance to concentrated ethanol fumes. Significant differences in tolerance were found among lines selected on different media which were consistent across the eight populations. On the 9% test media, the 6% and 9% selection lines, as compared with the control lines selected on 0% ethanol, were more likely to survive as pre-adults or adults, faster to develop as preadults, and heavier and more productive as adults. However, the tolerance of the 3% lines to the 9% test media was less than that of the 0% control lines in preadult and adult survival, intermediate between that of the 0% and the 6% and 9% lines in productivities, and apparently superior to the 6% and 9% lines in development times and adult weights. The 3%, 6% and 9% lines showed similar tolerances to the ethanol vapour. Previous work showed that 3% ethanol can be a metabolic benefit to D. melanogaster but 6% and 9% are metabolic costs. The present results suggest that the phenotype selected on 3% to obtain a metabolic benefit differs in many respects from that selected on 6% and 9% to minimise their detrimental effects.