ABSTRACT
Ethanol and acetic acid tolerances were compared in a French, highly tolerant population, and in a Congolese, very sensitive population. For both tolerances, chromosome substitutions demonstrated a major effect on chromosome 3, a lesser effect on chromosome 2, and no effect on chromosome 1, except in interactions. Directional selection experiments led to significant increases of tolerance to both toxics. Of greater interest, a strong correlated response was observed in each line: increased ethanol tolerance was accompanied by higher acetic acid tolerance and vice versa. A high genetic correlation (average value r = 0.77) was found between the two traits. These data suggest that alcohol dehydrogenase (ADH) activity does not play a major role in explaining the physiological differences known between Afrotropical and European populations. The metabolic flux permitting the detoxification of ethanol and acetic acid seems to be mainly controlled by acetyl-coA synthetase (ACS) at least in adult flies. Acetic acid adaptation could be as important as ethanol adaptation in the ecology of Drosophila melanogaster and other Drosophila species.
