Evolution and distribution of the coregonids

Increased knowledge of the morphological and physiological plasticity of the coregonids has minimized the significance of conflicting morphological data that have retarded the development of an evolutionary theory. Of the four phyletic lines recognized through worldwide studies,Coregonus originated in the lake and stream area of northwest Eurasia, Stenodus andProsopium evolved in the rivers of Siberia and northwest America respectively, and Leucichthysbecame differentiated in the lake-studded area of northeast America. Isolation and range extension were facilitated by events of the Pleistocene epoch. Inter-continental exchange most likely took place in the Bering Strait region. Representatives of each group in its area of origin are highly variable. Range extensions of each group are characterized by lesser morphological variability and at the extremes only one or two relatively stable species remain.