CYTOLOGICAL ABNORMALITIES PRODUCED BY EXPERIMENTAL TEMPERATURE SHOCK ON TRITURUS TOROSUS EMBRYOS

Abstract

1. A study of the incidence of chromosomal mosaicism and abnormalities of mitosis has been made, utilizing tail-tip preparations made from larvae of Triturus torosus subjected early in development to low temperature. 2. Three hundred-ninety two "first" tail-tips and 294 regenerated "second" tail-tips have been studied cytologically from preparations made in 1948. An additional 27 preparations made in 1942 have also been studied. Similar observations were made in 1948 on tail-tips from 582 control T. torosus larvae. 3. The experimental larvae were exposed to low temperatures (0 to 8° C.) for varying periods of time (45 minutes to 23 hours) at stages of development from 5 minutes after insemination, through blastula, gastrula, neurula and tail-bud stages. 4. No haploid or polyploid individuals were observed, in either the control or experimental groups. 5. Of the 392 "first" tips, 153 (39 per cent) were normal diploids; 156 (40 per cent) had nuclei of variable size or variations in nucleolar number; 79 (20 per cent) had abnormal mitoses; and 4 (1 per cent) were chromosomal mosaics. Of the 294 "second" tips, 71(24 per cent) were normal diploids; 107 (36 per cent) had nuclei of variable size or variations in nucleolar number; 102 (35 per cent) had abnormal mitoses; and 14 (5 per cent) were chromosomal mosaics. Of the 27 tips prepared in 1942 from cold-treated animals, 5 were clearly diploid, 11 had nuclei of variable size or variations in nucleolar number, 6 had abnormal mitoses, and 5 were chromosomal mosaics. In general, the incidence of all types of cytological abnormality was higher in the regenerated than in the "first" tips. This incidence of abnormality is significantly higher than that found in the controls. 6. The types of mosaics found included: hypodiploid/diploid/hyperdiploid; diploid/hyperdiploid; diploid/triploid; diploid/triploid/tetraploid; diploid/triploid/pentaploid; diploid/tetraploid. 7. A wide variety of abnormalities of mitosis was noted, including: "sticky" anaphases and telophases; anaphases and telophases with lagging or lost chromosomes or chromosome fragments; anaphases and telophases with bent spindles; multipolar spindles. Masses of relatively uncondensed chromatin and interphase nuclei with persistent connections between the daughter components were also present. 8. The evidence indicates that T. torosus larvae exposed early in development to low temperatures may suffer quite radical changes in chromosome number in some body cells, as well as less extreme abnormalities of mitosis. This is in accord with the findings of other workers for other species, and offers a clue to the possible mode of origin of the cytological abnormalities observed in T. torosus embryos subjected to shipment in an ice-and-water mixture.