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males, the presence of an anterior process of the basioccipital bone, and division of the 

 preoperculomandibular canal. Nine species were recognized in Phoxinus, including P. 

 brachyurus, phoxinus, issykkulensis, neogaeus, tennesseensis, cumberlandensis, oreas, eos, 

 and erythro 'gaster : 



Two-hundred and ten transformation series were analyzed and polarized based mainly on 

 outgroup comparison to evaluate the phylogenetic relationships among species of Phoxi- 

 nus. The phylogenetic relationships of the species within the genus Phoxinus were resol- 

 ved based on the 210 transformation series by PAUP (v.3.0). In Phoxinus, two major 

 groups were recognized as the brachyurus- and the erythrogaster-cla.de. The brachyurus- 

 clade consists of the three Eurasian and one North American species: P. brachyurus, is- 

 sykkulensis, phoxinus, and neogaeus. Members of the erythrogasfer-cla.de are the other 

 five North American species, i.e., P. cumberlandensis, tennesseensis, oreas, eos, and 

 erythrogaster. 



Three hypotheses on the geographic relationships of the freshwater fish faunae in North 

 America and Eurasia were reviewed and compared. These are the "trans-Atlantic'\ the 

 "old Pacific connection", and the "Bering land connection" dispersal hypotheses. None of 

 these hypotheses could explain the geographic distribution of Phoxinus. A "Bering land 

 connection" vicariant hypothesis was proposed here to interpret the genus' geographic dis- 

 tribution. The Bering land connection vicariant hypothesis proposed that the submergen- 

 ce of the Bering land bridge during the Miocene caused the speciation of the ancestor of 

 Phoxinus, while the interruption of the bridge during the Pliocene split the ancestor of the 

 Phoxinus species complex. This hypothesis was well supported by the alloelectrophoretic 

 studies of Joswiak (1980). The speciation within the erythro gaster-c\dAe and the phoxi- 

 nus species pair might be due to some vicariant events and/or adaptation to the habitats. 



