Selection at the alcohol dehydrogenase locus of Drosophila melanogaster: effects of ethanol and temperature.

Drosophila melanogaster larvae were subjected to 10 generations of selection on 6% ethanol at 17, 25, and 30 degrees C. For each temperature there was a significant (P less than 0.01) increase in the frequency of the Adh isoallele. Controls with no ethanol showed no change in the frequency of the AdhF isoallele. Larvae subjected to stronger selection on 8% ethanol confirmed the results. When adults of various ages were subjected to 16 and 32 degrees C, the ADHF isoenzyme retained its twofold advantage in activity over ADHS regardless of the temperature. The same result was obtained with larvae at 16 and 35 degrees C. Although some effect of temperature was demonstrated, it was concluded that the effect was not strong enough for temperature to be a selective factor under the conditions studied. However, ethanol is a strong selective factor for laboratory populations.