EFFECTS OF VARIOUS LEVELS OF X-IRRADIATION ON THE GAMETES AND EARLY EMBRYOS OF FUNDULUS HETEROCLITUS

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Abstract
Gametes and early embryonic stages of F. heteroclitus were X-irradiated with doses of 300 r to 200,000 r. The 1st cleavage was sensitive to doses above 300 r while sperm, exposed to 200,000 r, were used successfully to fertilize normal eggs which then developed into normal embryos, a few of which were able to hatch. Such embryos may have been haploids, developing parthenogenetically from irradiated sperm. Some eggs exposed to 100,000 r were fertilizable and a few developed to stage 17 without obvious teratologies. Subsequently these embryos developed circulatory and nervous abnormalities and none hatched. Stages following the highly sensitive first cleavage showed progressive tolerance to irradiation with stage of development. The blastula was able to continue normal development after 1000 r. Anterior neural structures were most affected by X-irradiation during the expansion of the gastrula. Point irradiation with alpha particles from polonium (20,000 reps) to one cell of the 2-cell stage rendered the embryo incapable of successful gastrulation. This may have been due either to mechanical interruption of morphogenetic movements or to an alteration in the blastoderm-yolk relations.