Prolonged environmental stress induces mutations and provides nonspecific adaptation of drosophila populations

Abstract

Adaptation of natural drosophila populations from the area radiocontaminated due to the Chernobyl accident (Vetka district of Gomel region) and from the control area (Berezinsky National Reserve) to irradiation was studied. Additional exposure to 40 Gy γ-rays resulted in different responses of population samples - much more dominant and recessive lethal mutations arose in the population from the control area than from that with "radiation history". Viability of flies from Vetka district was much higher after additional irradiation in comparison with flies from Berezinsky Reserve. These facts prove that Vetka population is more resistant to radiation than Berezinsky one. When the population samples were kept under laboratory conditions without irradiation for 8 generations it was revealed that the mutation level in both populations increased at keeping under such conditions. Adaptation of Vetka population to irradiation remained, besides, the control population also became more resistant to ionizing radiation. It means that keeping of natural drosophila populations under laboratory conditions is a strong stress (limited space, overpopulation, other temperature and light conditions), which increases a mutation process and induces non-specific adaptation. In order to study the process of insect adaptation in detail we investigated experimental drosophila populations of 4 kinds: control, supplied with melanin, irradiated in each generation and irradiated with melanin. The samples of these populations were exposed to 30 Gy x-rays in the 55th generation. Dominant and recessive lethal mutation frequencies, induced by additional radiation exposure, were the lowest in the irradiated population - this population was best adapted to ionizing radiation impact. The population irradiated with melanin was less resistant. This may be explained by a radioprotective action of melanin - more radiosensitive genotypes were not eliminated by natural selection and remained in the population preventing its adaptation. Thus melanin which is an effective radioprotector against chronic irradiation is able to prevent adaptation process. © 2006 Springer.