The fate of polymorphic inversions of Drosophila melanogaster transferred to laboratory conditions.

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Abstract
Three Japanese natural populations of D. melanogaster were transferred to laboratory cages and kept at 3 temperature conditions (25.degree. C constant, 20 .apprx. 30.degree. C fluctuating and 18.degree. C constant). Their chromosomal variation was examined after about 20 mo. Polymorphic inversions found at high frequency in nature were almost eliminated from the cage populations at 25.degree. C and 20 .apprx. 30.degree. C condition, and were in the process of being eliminated at 18.degree. C. The elimination of the polymorphic inversions was confirmed in the periodical monitor of cage populations. Inversions were disadvantageous compared to the standard chromosomes in laboratory cages, and the selection coefficient of the average inversion was 0.05 or 0.06 for the heterozygotes and 0.10 or 0.12 for the homozygotes. The direct estimates of fitness components showed that the inversion chromosomes had various selective values in productivity but they had relatively constant selective values in viability which might result in the elimination of inversions. The frequency of unique (newly occurring) inversions in cage populations was equal to that found in nature, 0.0026/major autosome arm per generation.