INTRASPECIFIC GENETIC-STRUCTURE OF WHITE SUCKER (CATOSTOMUS-COMMERSONI) IN NORTHEASTERN NORTH-AMERICA AS REVEALED BY MITOCHONDRIAL-DNA POLYMORPHISM

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to study the influence of Pleistocene glaciations on the in traspecific genetic structure and distribution of the white sucker (Ca tostomus commersoni) in northeastern North America. A total of 312 whi te sucker from 13 populations, including a population of dwarf ecotype s (Catostomus commersoni utawana), were analysed. An average of 93 fra gments per individual and 40 haplotypes were generated by nine restric tion endonucleases. Four discrete clades were identified but the major ity of the genotypes found (70%) were not associated with any of the c lades. The phylogenetic continuity and the geographic admixture of som e of the few clades identified are associated with the extensive distr ibution of the species south of the ice sheets during Pleistocene glac iation events. Hierarchical analysis of the variability in mtDNA revea led a significant regional subdivision to the northwest and southeast of the St. Lawrence drainage system and significant structure at the p opulation level. As the dwarf form exhibited a haplotype identical to that found among normal forms, we tentatively conclude sympatric diver gence as the most likely origin of the dwarf and normal ecotypes sampl ed in the Adirondacks.