Association of Chromosome and Enzyme Polymorphisms in Natural and Cage Populations of DROSOPHILA MELANOGASTER

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The frequencies of a polymorphic inversion, In(2L)t, and of Adh and αGpdh alleles were analyzed in three natural populations of Drosophila melanogaster from Japan. Significant positive correlations between the frequencies of In(2L)t and AdhS or αGpdhF were detected due to tight linkage. An analysis of correlation with latitude showed that the negative cline of AdhS frequency could be explained entirely by its linkage with In(2L)t; the frequency of AdhS on the standard chromosome did not show a latitudinal cline. To the contrary, the cline of αGpdhF 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 αGpdh alleles were close to those in earlier cage populations of the same geographical origin.

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