A MULTILEVEL APPROACH TO THE SIGNIFICANCE OF GENETIC-VARIATION IN ALCOHOL-DEHYDROGENASE OF DROSOPHILA

Prior studies showed that differences in alcohol dehydrogenase (ADH) a ctivity across genotypes of Drosophila are decisive for the outcome of selection by ethanol. In the present paper, the effect on ADH activit y and egg-to-adult survival of combinations of ethanol, propan-2-ol, a nd acetone in naturally occurring concentrations is examined. Propan-2 -ol is converted into acetone by ADH in vitro. Acetone is considered a competitive inhibitor of ethanol for the ADH enzymes. The melanagaste r-ADH-S allozyme is two times more sensitive towards inhibition by ace tone than either simulans-ADH or melanogaster-ADH-F. The physiological implications of these in vitro differences for larvae were studied in short-term in vivo and long-term exposure experiments. No major diffe rences in acetone accumulation or fitness parameters were found betwee n the strains in response to ecologically relevant concentrations of a cetone or propan-2-ol. Ethanol, however, strongly decreased egg-to-pup al survival in both Drosophila simulans strains and increased developm ental time in four out of the five strains tested. Therefore, under ph ysiological conditions only ethanol was shown to act as a selective ag ent on the ADH polymorphism during egg-to-pupa development in Drosophi la.