558 



HYBRIDIZATION AND EARLY DEVELOPMENT 



Hamburger, 1956, has hybridized three European species of Triton, namely crlstatus, 

 taenlatua (formerly viilgarle) and palmatua (formerly helveticus). The crosses were made 

 both ways but some were more viable than others. Eecently ( 19^+7 ) Connon hybridized three 

 species of California Tritons, namely tisrosus, rivularis, and granulosa (formerly simi- 

 lans, Twitty, 19'<-2). If the oviduct of the ovulating Urodele is opened and the eggs are 

 transferred into a concentrated sperm suspension in Standard Solution, hybridization can 

 be achieved. In these forms where development can be carried quite far, the inheritance 

 of pigment patterns may be studied as they are influenced by maternal and paternal genes. 



By combining hybridization with androgenesis Porter (19'*-l) has ingeniously discovered 

 that there are two (morphological) varieties of Rana piplens. One he collected in Vermont 

 and the other near Philadelphia. These differences are not normally found, even though 

 the crosses may be frequently made, because in. normal hybrids the nuclear differences are 

 compensated for by the cytoplasmic differences and the resulting larvae are normally 

 viable.* 



OBSERVATIONAL AND EXPERIMENTAL DATA : 



Materials for an hybrid cross from each of tEe groups on the preceding page should 

 be made possible by the Instructor. The results should be analyzed with respect to (a) 

 Bate of cleavage (b) Type of cleavage (c) Stage of breakdown. 



If x-ray facilities are available, it is instructive to irradiate the spermatozoa of 

 any of the crosses In Group 2 on the preceding page with at least 10,000 r units prior 

 to the insemination of the eggs of the other species. Generally some of these eggs will 

 pass the critical stage of gastrulatlon. (See Eugh eind Exner, 1959- ) 





P 





I « I I 



I i. ,i .1 





I 





* X I 





J,- 5,1 

 :• f. ^ 



Fig. 1. A typical Rana piplens female. Fig. 2. A tj-pical Rana burns! female. Figs. 3 to 



6i Hybrids from various crosses. Fig. '3. piplens female x piplens male. Fig. 4. burnsl 



female x burnsl male. Fig. 5. piplens I'emale x burnsl male. Fig. 6. burns! female x 



piplens male. 



In Figs. 5 and 6 note that the burnsl joung have spots on tJie hind legs. This Is probably 



Indication of their heterozygous (Bb) nature. In Fig. 4 some of the burnsl have spots on 



the hind legs (upper row) while the two at the lower left are devoid of the black leg 



spots. The former are probably Bb and the non-spotted. 



Figs. 7 and 8 - two types of tadpoles, spotted and non-spotted. The spotted tadpoles In 



most cases give rise to piplens young, and the non-spotted tadpoles, In most cases, give 



rise to burns! young. 



(Courtesy J. A. Moore I92I+: G«netlc8 27:'+08) 



