Inversion Polymorphisms in Populations of Drosophila Melanogaster in the South-West Islands of Japan: Comparisons with the Mainland Populations

Natural populations of D. melanogaster newly collected from the South-West Islands of Japan were examined for the frequencies of inversions, and the results, together with previous data, were compared with those of the mainland populations. The four Common cosmopolitan inversions (2Lt, 2RNS, 3LP, 3RP) were detected from most of the populations with higher frequencies. The three Rare cosmopolitan inversions (3LM, 3RC, 3RMo), three Quasi cosmopolitan inversions (2LA, 3LY, 3RK) and two new Endemic inversions were also found but with lower frequencies. Some of the South-West Island populations still maintained higher levels of inversion polymorphisms compared to the mainland populations, while others lost the polymorphisms to various degrees. The South-West Island populations were characterized by the higher frequency of In(3L)P. The ratios of In(3L)P/In(3R)P in the South-West Islands are significantly higher than those of the mainland populations, suggesting that the In(3L)P is relatively adaptive in the South-West Islands.