GENETIC AND MORPHOLOGICAL-DIFFERENTIATION BETWEEN DWARF AND NORMAL SIZE FORMS OF LAKE WHITEFISH (COREGONUS-CLUPEAFORMIS) IN COMO LAKE, ONTARIO

Normal and dwarf size forms of lake whitefish (Coregonus clupeaformis) from Como Lake, Ontario, were sampled at spawning time and examined f or differences in electrophoretic, mtDNA, and morphological characteri stics to test the hypothesis of reproductive isolation and provide clu es regarding evolutionary origin. Of the 36 enzyme loci examined, 33 w ere fixed for the same alleles in both dwarf and normal lake whitefish . At the three polymorphic loci, allele frequencies were not statistic ally different between dwarfs and normals. mtDNA analysis revealed fiv e different haplotypes. The same mtDNA haplotype was the most common i n both dwarf and normal lake whitefish, but there was a statistically significant difference in haplotype frequencies between the two size f orms. Discriminant and principal component analyses demonstrated highl y significant morphological differences between dwarfs and normals. Be cause the two size morphs spawn in the same place at the same time, it is most likely that genetic differences, not different rearing enviro nments, underly the observed morphological differences. mtDNA haplotyp es derived from both the Mississippi and Atlantic glacial refugia are present in Como Lake lake whitefish, raising the possibility of an all opatric divergence for the two forms; however, this hypothesis require s testing by genetic comparisons of other sympatric populations in Ont ario.