The Differentiation of Populations | 215 



eastern and western genotypes of both Z A and Z B has occurred. 

 Woodson interprets the eastern subspecies to be in the process of 

 genetic submergence by the western one, since its western move- 

 ment is proportionately less. Nevertheless, its effects on the western 

 leaf shape can be clearly seen. 



Clinal Variation in Animals. In some cases, although the geo- 

 graphic variation is continuous, experimental evidence indicates 

 that a considerable amount of differentiation has occurred. Variation 

 in the leopard frog, Rana pipietis, is extensive and discordant. The 



Fig. 10.1 I Map showing distribution of AscZeptas fufoero^fl. Each 

 symbol represents a county record. Large dots, A. t. interior; small dots, 

 A. t. tuherosa; hollow circles, putative hybrids between subsp. tuberosa 

 and subsp. interior; half-circles, A. t. rolfsii. {From Woodson, 1947, Ann. 

 Missouri Bot. Qard. 34. ) 



