THE "HERTWIG EFFECT" IN TELEOST DEVELOPMENT

¹ Marine Biological Laboratory, Woods Hole, Mass.
² Dept. of Radiology, Columbia University, New York 32, New York

1. Mature sperm of Fundulus heteroclitus were exposed to ionizing radiations from Cs.-137 at the rate of 5000 r/min., for doses ranging from 5000 r to 150,000 r, and were then used to fertilize normal eggs of the same species. Control eggs from the same batch were inseminated with unirradiated sperm from the same source.

2. While variations in normal fertilizability of the control eggs do occur, associated with the season and breeding activity, in every case some eggs were fertilized and developed following insemination with sperm which had been exposed to every dose level. This was not mere activation since cleavages followed.

3. The presence of irradiated (sperm) chromatin had no effect on the time or nature of the early cleavages. The initial adverse effects were noted at the time of gastrulation.

4. Exposures of sperm to 500 r had no apparent effect on the development of eggs, while exposures to 5000 r caused high mortality and morbidity, and above 5000 r (to the sperm) the effect of ionizing radiations appeared to decrease so that a greater percentage of near-normal embryos resulted from cleaving eggs.

5. The fact that a few specimens from 50,000 r or more sperm could not be readily distinguished from the controls suggests that complete recovery of diploidy may sometimes occur after activation. This was substantiated by cytological examination.

6. While parthenogenesis does not, or need not, occur naturally for this species, the fact that it can occur is of biological significance, suggesting that all vertebrates may possess eggs with such regulatory potentialities.