“…(b) Natural populations of D. melanogaster are generally polymorphic for electrophoretic variants of ADH: ADH-F and ADH-S (Ursprung and Leone, 1965;Ward and Hebert, 1972;Pipkin et a!., 1976), AdhF allele persisting in some cases at higher frequencies in habitats where ethanol is present at higher concentrations (Briscoe et a!., 1975;Hickey and McLean, 1980 Ward, 1974Ward, , 1975Oakeshott, 1976a, b;Kamping and van McDonald and Ayala, 1978;Birley eta!., 1981;Sampsell and Steward, 1983;Kerver and van Delden, 1985). Additionally, the homozygous FF individuals usually have higher fitness on ethanol supplemented media than the SS ones (Gibson and Miklovich, 1971;Libion-Mannaert eta!., 1976;Oakeshott, 1976a;Thompson and Kaiser, 1977;Kamping and van Delden, 1978; van Delden and Kamping, 1983;Dorado and Barbancho, 1984).…”