The adaptive response of the Adh locus to different temperatures was determined in an experimental population with a stabilized gene pool in order to confirm the conclusions reached in a previous paper (Pieragostini et al., Genetica 56: 27-37, 1981) using as experimental material a laboratory population in which heterosis and strong interaction between loci were present.
By sampling a stable lab population, three cage populations were constructed, heterozygous at the Adh locus and genetically identical but reared at different temperatures (P 18 ° C, P 25 ° C and P 28 o C). On these populations we studied the dynamics of Adh allele frequencies and of five metric traits up to the fifth generation of caging. The most interesting result is represented by the differences between P 28 °C and the other two populations (P 25 °C and P 18 °C). In particular P 25 °C and P 18 °C show a strong similarity with the original population both in Adh allele frequency and relationship between Adh genotype and the respective metric phenotype; this is not the case for P 28 o C which differed from the original population and the other two newly founded ones not only in Adh allele frequencies but even in gene arrangements.
Comparing these results with those obtained in the previous work it can be concluded that Adh frequency variations can be a side effect of the evolutionary pattern of the populations which in turn depends on the initial genetic composition.