Response of Eggs of Heterocypris incongruens (Ostracoda) to Experimental Stress

Abstract

The effects of freezing, drying, high temperatures, or various combinations of these on the eggs of the fresh-water ostracode Heterocypris incongruens were studied. In addition, the fate of 2,662 eggs of known parentage and time of laying was followed for 125 days. The results of the environmental experiments show that the eggs remain viable after drying at both 22.degree. C and 40.degree. C, and after frozen wet or dry at -18.degree. C. Eggs maintained wet at 40.degree. C did not hatch. The result of the known parentage experiment showed that H. incongruens produces two types of eggs; one type develops and hatches within 10 days of laying, and another remains dormant for varying periods of time after being produced. Both types of eggs may be produced by the same individual, although individuals may produce only dormant eggs. No female produced only rapidly developing eggs. There is no discernible pattern in the production of the two egg types, and the production of dormant eggs does not depend on recognizable changes in environmental factors. Furthermore, neither the age of the parent nor the number of eggs produced by her affects the type of egg laid. Eighty-five percent of the eggs produced are dormant with only a few capable of hatching whenever conditions are suitable for growth. For an animal living in temporary ponds and seeps this means that some eggs are always in effect monitoring the environment for suitable hatching conditions. If these conditions occur and do not persist long enough for the hatchlings to reach maturity, other eggs will still be viable and available for hatching when favorable conditions return again.