Radioresistance in natural populations of Drosophila nebulosa from a Brazilian area of high background radiation.

D. nebulosa, collected in two woods of a high background radiation area (both in Iron Hills, State of Minas Gerais, Brazil), were compared to and found to be more resistant than flies collected as controls in two other woods of an adjacent area. This was the second time that average differences in radioresistance between natural populations were established. Previous experiments were carried out with D. willistoni, in the same area and in comparable fashion. In spite of their higher radiation resistance the flies from the radiation area carried a higher expressed load than the controls. The following tests were performed to estimate the differences: (a) survival, after whole body exposure to 90 000 R of 60Co-gamma-rays on 120 strains set up from single inseminated females and (b) reproductive performance, in 240 duplicate croses, measured in terms of the difference between irradiated series (males received 3000 R of 60Co-gamma-rays) and their unirradiated counterparts. The data are based on an offspring of 293784 individuals. Futhermore, two diallel crosses between sensitive and resistant strains have shown that the differences probably are due mainly to additive genes.