Abstract
Four common cosmopolitan inversions (2Lt, 2RNS, 3LP, 3RP), four rare cosmopolitan inversions (2LA, 3LM, 3RC, 3RMo) and two recurrent endemic inversions (2LW, 3LY) were found to be distributed in Japanese natural populations of Drosophila melanogaster. Moreover, seventeen unique endemic inversions were rather randomly detected in many natural populations as well as in stocks that originated from small number of wild caught flies. The frequency of inversions was generally higher in Southern populations than in Northern populations, especially in the case of In(3R)P. The polymorphic inversions did not show any heterosis in the present analysis. The frequencies of inversion heterozygotes were almost equal to the expectaions with a few exceptions of a scarcity of the heterozygotes over the expectation. In the Katsunuma population, some inversions decreased remarkably within ten years, which resulted in the change of abundance order among four common cosmopolitan inversions. This kind of change might have occurred in the Shiojiri population. Both populations are very interesting in that new inversions are increasing in frequency and replacing the old ones.
