ASSOCIATION OF CHROMOSOME AND ENZYME POLYMORPHISMS IN NATURAL AND CAGE POPULATIONS OF DROSOPHILA MELANOGASTER

The frequencies of a polymorphic inversion, In(2L)t, and of Adh and alphaGpdh alleles were analyzed in three natural populations of Drosophila melanogaster from Japan. Significant positive correlations between the frequencies of In(2L)t and Adh(S) or alphaGpdh(F) were detected due to tight linkage. An analysis of correlation with latitude showed that the negative cline of Adh(S) frequency could be explained entirely by its linkage with In(2L)t; the frequency of Adh(S) on the standard chromosome did not show a latitudinal cline. To the contrary, the cline of alphaGpdh(F) frequency itself was positive, and its linkage with In(2L)t makes the positive cline unclear. These results suggest that the two allozymes themselves respond to latitudinal natural selection in different ways. When these populations were transferred to laboratory cages and maintained for a long time, they lost the chromosomal polymorphism but retained stable enzyme polymorphisms, although allele frequencies in the cage were not the same as in nature. The frequencies of Adh and alphaGpdh alleles were close to those in earlier cage populations of the same geographical origin.