TEMPERATURE INDUCED HETEROPLOIDY 



147 



DISCUSSION: 



Heteroploidy in plants has long been recognized but not until recently has its, normal in- 

 cidence among animals been determined (See Fankhauser's excellent review in 1945 Quart. 

 Rev. Biol. 20:20). It is now believed that triploidy in Triturus viridescens occurs nat- 

 urally to an extent of about 0. 7%. Some batches of eggs (or, more accurately, eggs 

 from certain females) will respond to cold treatment by producing almost 100% triploids, 

 among those which survive the treatment. It must be emphasized that the mortality of 

 all eggs, treated by these extremes of temperature, is very high, often as much as 50%. 

 It is now believed that the temperature shift at this particular time in maturation affects 

 the kinetic movements of maturation so that the formation of the second polar body is 

 suppressed. It is difficult to explain the infrequent haploids achieved by this treatment, 

 but the vast majority of aberrations are in the direction of triploidy, tetraploidy, etc. 

 The survival of Rostand's (1936) hybrids beyond the normal stage of termination of devel- 

 opment, following exposure to cold, fits in perfectly with the concept of polar body reten- 

 tion and the further possibility that amphimixis (in this case, with the foreign sperm) is 

 prevented. If the drastic temperature treatment is delayed for more than 30 minutes 

 (Triturus viridescens) the larvae which result are all diploid. 



Metaphase chromosomes from epidermal 

 cells of a haploid, a diploid and a 

 triploid tail -tip (11, 22 and 33 chromo- 

 somes). Tracings of enlarged photo- 

 micrographs. 



Nuclei of epidermis cells from a haploid, a 

 diploid and a triploid tail -tip. The size of 

 the nuclei is roughly proportional to the 

 number of chromosomes they contain. 

 Camera lucida drawings. 



Pigment pattern on the head of a haploid, 

 a diploid and a triploid larva, 4 weeks 

 old. Tracings of enlarged photomicro- 

 graphs. 



The same larvae as shown in Figure 3. 

 The haploid larva (left) is dwarfed and 

 edematous, the triploid is slightly larger 

 than the diploid. Tracings of enlarged 

 photom ic rographs. 



TRITURUS VIRIDESCENS 



From Fankhauser 1939: Proc. Nat. Acad. Sci. 25:233 



