144 



TEMPERATURE INDUCED HETEROPLOIDY 



FOR ANURA 



Anuran eggs should be secured from an ovulating female, pituitary-induced. 

 The eggs should be inseminated in the normal manner, flooded within 5 minutes, 

 and transferred abruptly to the low (or high) temperature in Standard Solution or 

 Spring Water. The eggs will stick to the bottom of the container (e. g. , finger 

 bowl or Petri dish) and the water may be poured off, and the water of a different 

 temperature added directly. The Anuran eggs need not be separated until after 

 the drastic temperature treatment, but at that time they must be separated into 

 finger bowls containing no more than 25 eggs per 50 cc. of medium, kept at tem- 

 peratures of 18°C. to 23°C. 



TEMPERATURES AND EXPOSURE PERIODS 



The time/temperature ranges for optimum results (highest heteroploidy with lowest mor- 

 tality) have not been determined. However, for the Urodele eggs an exposure of about 5 

 hours at about 3. 0°C. or an exposure of about 15 minutes at 35. 0°C. may be considered 

 as optimum until exact data are available. For the Anura, the only reference is Briggs 

 (1947) who suggests that 4 minutes at 37. C. seems to be highly productive of triploidy. 



Rostand (1933, 1934, 1936) found that hybrids between Hyla, Bufo, and Rana which nor- 

 mally go to pieces during cleavage or early blastula stages, will respond to the cold treat- 

 ment by producing some larvae. This type of experiment indicates that the Anura (as well 

 as the Urodela) will react to low temperatures by altering the chromosomal conditions 

 and thereby obviate the deleterious effects of foreign chromosomes. If various genera 

 (or species) of Anura are available, such attempts should be made to carry normally non- 

 viable hybrids past the critical stage of gastrulation. 



Diagram of hypothetical effect of low temperature 

 treatment on freshly fertilized salamander eggs. At 

 the time of fertilization, the amphibian egg hos given 

 off the fir^ polar body; the second maturation division 

 has reached metaphase and remains in this stage until 

 fertilization occurs. Refrigeration presumably sup- 

 presses the second maturation division and produces a 

 diploid egg nucleus. 



From Fankhauser 1942; Biol. Symposia 6:21 



o 



KOONO UAIVKAnOM 



