“…In the case of the alcohol-dehydrogenase (Adh) locus in Drosophila, however, there is now substantial agreement that the differences between alleles at this locus can have adaptive significance in a number of species (Gibson, 1970;Clarke, 1975;David, 1977;Starmer et al, 1977;Fontdevila et al, 1980;Knoppien et al, 1980). Thus in D. melanogaster, the frequently reported clines in Adh allele frequencies apparently have a selective origin (Pipkin et aL, 1973), whereby one agent of selection is temperature, a temperature-correlated variable perhaps relating to resources, or a combination of the two (Malpica & Vassalo, 1980). Considering resources, in polymorphic populations the Adh F allele is often favoured in the presence of alcohol (Gibson, 1970;Cavener & Clegg, 1978).…”