Selection against Adh null alleles in Drosophila melanogaster

Populations of Drosophila melanogaster polymorphic for an Adh null and an Adh positive allele (either Adhs or AdhF), were founded on regular food, on food supplemented with ethanol and on food suplemented with methanol. On ethanol-supplemented food Adh null was rapidly eliminated, but on regular food and on food supplemented with methanol a consistent decline in the frequency of the Adh null allele was also observed. Estimates of fitness, based on the rate of elimination of Adh nulls in the polymorphic populations were compared with estimates derived from egg-to-adult survival of F2's from crosses between homozygotes for Adh null alleles and homozygotes for Adh positive alleles. On 1-pentene-3-ol a rise in Adh null frequency was observed. Even in the absence of alcohol stress the Adh null genotypes are at a selective disadvantage which is relevant to the metabolic role of ADH and the Adh polymorphism in natural populations