Population dynamics of movable genetic elements in Japanese natural populations of Drosophila melanogaster. I. Microevolution of male recombination determinants in experimental populations.

Five natural populations of D. melanogaster in Japan were surveyed for male recombination frequency in terms of the quantities of the mean and variance after crossing with cn bw females. The experimental condition enabled P-M system hybrid dysgenesis to take place. The means were not so different from one another, but there was a vast variation in the variances between them. Using one of these populations, two additional experimental populations were started, and the male recombination frequencies were monitored for 30 generations. Both the means and variances decreased in value at 25°C. The regression line was Y=-0.000030X+0.001706 on generation for the mean values, and was Y=-0.000098X+0.005068 for the standard deviations in the cage population. There was no correlation between the means or the standard deviations and the copy numbers of the members of P element family as a whole. The experimental results indicate that the complete P transposable elements still retained in population were decreased in frequency and replaced by its degenerative nonautonomous forms.