THE EFFECTS OF CONTINUOUS GAMMA RADIATION ON THE INTRINSIC RATE OF NATURAL INCREASE OF DAPHNIA PULEX

The effects of continuous sublethal Co/sup 60/ radiation on the intrinsic rate of natural increase, r, was studied. An analysis was also made of the effects of radiation on the population attributes underlying r, namely, birth rate, b, death rate, d, and stable age-distribution. Each of 18 experimental populations was exposed to a different, continuous dose rate, ranging from 25 to 75 r/hr. The results showed that r decreased continuously as a nonlinear function of the dose rate (although st run. Concent a linear function of the square of the dose rate). The effects of increasing dose rate on the stable age- distribution were mainly a decrease in the proportion of individuals in the youngest age groups and an increase in the proportion of older individuals. The overall results indicate that the reduction of fecundity and fertility was due to direct effects of the radiation on the ovaries rather than to indirect, physiological effects. It was considered likely that dominant lethal chromosome aberrations were uitlmately responsible. Individual life expectancy at birth, or average life-span, was not greatly shortened by any of the dose rates employed. Furthermore, age-specific survival rates were not affected until late in reproductive life. Individual growth inmore » length increased with increasing dose rate. (TCO)« less