148 



Fig.95: Composite distribution for the ranges of species of Phoxinus in North America. (Data sum- 

 marized from Lee et al. 1980.) 



only in a small area of Uli River of Xinjiang (China) and of Kazakhstan in Asia (Berg 

 1949, Yang & Huang 1964, Reshetnikoo & Shakirova 1993). 



I hypothesize that the ancestor of the P. phoxinus complex might have occurred in Asia 

 and dispersed from Asia into North America through the Bering land connection in (or 

 before) the Pliocene, otherwise it would be difficult to interpret the origin of P. neogae- 

 us. The ancestor of Phoxinus species complex is proposed to have been separated into 

 Asian portion and North American portion, by the submission of the Bering land connec- 

 tion during the Pliocene. The alloelectrophoretic studies on allozymes of Phoxinus (Jos- 

 wiak 1980) showed this separation might have taken place about eight million years ago. 

 The Asian portion of the ancestor was speciated into P. issykkulensis which occurs only 

 in Lake Issyk-ku of Kazakhstan, and phoxinus which occurs in Asia and Europe. The fish 

 fauna in the Lake Issyk-kul shows that the Lake Issyk-kul was isolated from its surroun- 

 ding (Reshetnikoo & Shakirova 1993) though when and how the isolation occurred is un- 

 certain. The speciation of the ancestor of "P. phoxinus + P. issykkulensis" might be related 

 to this vicariant event. 



The North American portion of the ancestor of the Phoxinus species complex was spe- 

 ciated into P. neogaeus, which prefers to live in boggy environment. P. neogaeus now oc- 



