8. HYBRIDIZATION AND EARLY 

 DEVELOPMENT 



PURPOSE: To demonstrate the effects upon early development of the egg when activated 

 by foreign spermatozoa, and to determine the relative influence of the maternal and 

 paternal factors in hybrids which pass the critical period of gastrulation. 



MATERIALS: 

 Biological: 



Ovulating females of any Amphibian species, and sexually mature males 



of a variety of species. (Pre-breeding, sexually mature females of 



any species of Amphibia can be induced to ovulate by pituitary injection. ) 



Technical : Standard equipment. 



METHOD: 



Precautions : 



1. Avoid contannination with sperm suspensions other than that intended for use. 

 All instruments and glassware should be sperm-sterile. 



2. Examine sperm suspensions under the microscope for motile spermatozoa. 



3. Cleaving eggs should be separated from others, and placed in finger bowls 

 of Standard Solution (or Urodele Growing Medium) at cool temperatures, not 

 more than 25 eggs per 50 cc. of medium per finger bowl. 



Controls : Eggs inseminated with spermatozoa of the same species. This should be 

 done after the hybridization experiments, to avoid contamination. 



Procedure : A summary (Moore, 1941) of the hybrid crosses between American 

 species of Rana follows: 



FEMALE 



NO 



CLEAVAGE 

 OCCURS 



DEVELOP TO 

 BEGINNING OF 

 GASTRULATION 

 ONLY 

 (Cleavage 



rate 

 maternal) 



< 



< 



Rana clamitans X 



Rana clamitans X 



Rana clamitans X 



Rana clamitans X 



Rana clamitans X 



Rana clamitans X 



Rana septentrionalis X 



kRana septentrionalis X 



Rana sylvatica X 



Rana sylvatica X 



Rana sylvatica X 



Rana sylvatica X 



Rana pipiens X 



Rana pipiens X 



Rana pipiens burnsi X 



Rana palustris X 



Rana catesbiana X 



MALE 

 Rana sylvatica 

 Rana pipiens 

 Rana palustris 

 Rana catesbiana 

 Rana septentrionalis 

 Rana hechscheri 

 Rana clamitans 

 Rana pipiens 



Rana pipiens 

 Rana palustris 

 Rana catesbiana 

 Rana sphenocephala 

 Rana sylvatica 

 Rana catesbiana 

 Rana sylvatica 

 Rana sylvatica 

 Rana pipiens 



WILL DEVELOP 

 PAST THE 

 STAGE OF 



GASTRULATION: 

 MAY EVEN 



METAMORPHOSE 



Rana pipiens X 



Rana pipiens X 



Rana pipiens X 



^ Rana pipiens burnsi X 



Rana pipiens burnsi X 



Rana sphenocephala X 



Rana sphenocephala X 



^Rana palustris X 



If Hyla or Bufo eggs or sperm are available, hybridization with Rana should be at- 

 tempted. In most, if not all, cases these hybrids would fall into the second group above. 



Rana palustris 

 Rana sphenocephala 

 Rana pipiens burnsi 

 Rana pipiens 

 Rana palustris 

 Rana pipiens 

 Rana palustris 

 Rana pipiens 



- 121 



