PRELIMINARY NOTE ON THE VARIATION OF SOME FITNESS FACTORS IN PERIODICALLY IRRADIATED DROSOPHILA MELANOGASTER POPULATION

Two populations of Drosophila melanogaster were irradiated periodically with small doses of x rays (100 r and 500 r). Two other populations were cultured as controls at the same time. All the populations were held at 19 deg plus or minus 1 deg C in a constant temperature room. On the 150th and 225th day the hatchability and the fertility were assayed on samples of eggs obtained from individuals, not directly irradiated, taken from each population. The relative data indicate a percertage diminution of these two fitness factors in the populations irradiated with 500 r and to a smaller extent in those irradiated with 100 r. The diminution in fitness is interpreted as being due to the accumulation of lethal genes induced by the irradiation. At intervals of 25 days the numerical levels were determined and this was carried out 17 times. The totals obtained in the 17 counts are significantly higher (with the X/sup 2/ test) in the populations irradiated with 500 r than in the controls and in those irradiated with 100 r. However, the test for heterogeneity was positive. If these observations are confirmed, they could be interpreted as being due to a greater adaptability in themore » irradiated populations in a selective environment. (auth)« less