PHYLOGENY OF 5 PROSOPIUM SPECIES WITH COMPARISONS WITH OTHER COREGONINE FISHES BASED ON ISOZYME ELECTROPHORESIS

Phylogenetic relationships of Prosopium gemmifer, P. spilonotus, P. wi lliamsoni, P. cylindraceum and P. coulteri species were determined bas ed on variation at 37 allozyme loci, and compared with Stenodus and ni ne species of Colegonus. Of the three genera, Prosopium was the most d istinct with Nei genetic distances to Coregonus of D=0.55-1.05 and to Stenodus of D=0.58-0.92. Stenodus and Coregonus were closely related b ut grouped as sister taxa with a mean genetic distance of 0.31 (range 0.22-0.40). These results agree with the degree of morphological diffe rentiation among the genera as well as with observations concerning hy bridization, e.g. many Colegonus species hybridize with Stenodus, but no natural hybrids are known between Prosopium and other coregonines. Within Prosopium, P. coulteri was the most divergent species branching out at D=0.51 from the others and followed by P. cylindraceum at D=0. 28. The three remaining species are closely related. Among them P. wil liamsoni joins P. gemmifer and P. spilonotus at 0.04, and the distance between the two Bear Lake endemics is only 0.004. The distance betwee n P. cylindraceum and the remaining Prosopium species is similar to di stances between Stenodus and Coregonus. The small genetic distance bet ween P. spilonotus and P. gemmifer suggests their recent divergence. E ven though no fixed differences were found between them, different all eles were present at two loci at large enough frequencies to indicate reproductive isolation. This confirms that P. gemmifer and P, spilonot us are good biological species as indicated by their distinct morpholo gy and ecology. (C) 1998 The Fisheries Society of the British Isles.