THE REPRODUCTIVE CAPACITY OF ARTEMIA SUBJECTED TO SUCCESSIVE CONTAMINATIONS WITH RADIOPHOSPHORUS ,

Abstract

1. This paper is a progress report on four additional years of studying Artemia in and from mass cultures to which radioisotope has been added. 2. Although the number of adults seen in mass cultures may be equivalent, subcultures of control and experimental strains react differently to radioisotope additions. Strains descended from ancestors exposed to P do not necessarily survive a second dose even though total dosage does not exceed the extinction dose given as a single addition. A period of recovery involving a passing of generations must intervene. Depending upon culture conditions, this may involve two to four years. 3. Pair mating tests revealed that in comparison with controls, experimental strains: A. Have a shorter life span. B. Deposit fewer zygotes per brood. C. Deposit more of their developed zygotes as viable cysts. D. Show poor survival to adulthood except when crowding is mitigated by low fecundity. 4. Because the frequency of brood deposit has been regular in both control and experimental strains, an increase in total progeny has accompanied increased life span. The one exception to an interval of three to four days between deposits occurred in 1965 records of a strain recovering from a near lethal dose. 5. The sex ratios among adult progeny from pair matings now favor females in all strains. 6. On the basis of pair mating tests, maintenance of mass cultures at an observed level of 300 adults per three liters requires only 0.2% of the reproductive potential of controls. Cultures of experimental origin utilize 1% or more of their potential to maintain the same total. 7. The proportional number of larvae surviving to adults may be critical in determining whether or not a strain can tolerate another exposure to a radioisotope. 8. Although general comparisons may be drawn to crowding experiments in insect populations, a complete parallel is impossible because of the shrimp's indeterminate growth pattern (although Artemia populations are inversely densitydependent).