Tolerance to 1-pentene-3-ol and to 1-pentene-3-one in relation to alcohol dehydrogenase (ADH) and aldo keto reductase (AKR) activities in Drosophila melanogaster

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

Prior studies showed that differences in alcohol dehydrogenase (ADH) activity across genotypes of Drosophila are decisive for the outcome of selection by ethanol. In the present paper, the effect on ADH activity and egg-to-adult survival of combinations of ethanol, propan-2-ol, and 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 melanogaster-ADH-S allozyme is two times more sensitive towards inhibition by acetone 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 differences in acetone accumulation or fitness parameters were found between the strains in response to ecologically relevant concentrations of acetone or propan-2-ol. Ethanol, however, strongly decreased egg-to-pupal survival in both Drosophila simulans strains and increased developmental time in four out of the five strains tested. Therefore, under physiological conditions only ethanol was shown to act as a selective agent on the ADH polymorphism during egg-to-pupa development in Drosophila.

The influence of Adh function on ethanol preference and tolerance in adult Drosophila melanogaster

Preference determines behavioral choices such as choosing among food sources and mates. One preference-affecting chemical is ethanol, which guides insects to fermenting fruits or leaves. Here, we show that adult Drosophila melanogaster prefer food containing up to 5% ethanol over food without ethanol and avoid food with high levels (23%) of ethanol. Although female and male flies behaved differently at ethanol-containing food sources, there was no sexual dimorphism in the preference for food containing modest ethanol levels. We also investigated whether Drosophila preference, sensitivity and tolerance to ethanol was related to the activity of alcohol dehydrogenase (Adh), the primary ethanol-metabolizing enzyme in D. melanogaster. Impaired Adh function reduced ethanol preference in both D. melanogaster and a related species, D. sechellia. Adh-impaired flies also displayed reduced aversion to high ethanol concentrations, increased sensitivity to the effects of ethanol on postural control, and negative tolerance/sensitization (i.e., a reduction of the increased resistance to ethanol's effects that normally occurs upon repeated exposure). These data strongly indicate a linkage between ethanol-induced behavior and ethanol metabolism in adult fruit flies: Adh deficiency resulted in reduced preference to low ethanol concentrations and reduced aversion to high ones, despite recovery from ethanol being strongly impaired.