A major sextet of mitochondrial DNA phylogenetic assemblages extant in eastern North American brook trout (Salvelinus fontinalis): distribution and postglacial dispersal patterns

Mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) of 2422 brook trout (Salvelinus fontinalis) from 60 units (major drainages , small stream catchments, and isolated lakes) representing 155 populations in eastern North America were examined to test hypotheses regarding postgl acial dispersal and recolonization. An analysis of molecular variance (AMOV A) indicated that 38.8% of the variation was partitioned among the units, w hile approximately 60% was distributed among populations (phi(ST) = 59.3) c ompared with 40.7% within populations. This distribution of variation sugge sts a large degree of heterogeneity in population founding events and phylo geographic structuring in this species. Comparisons of mtDNA diversity betw een fish from putative refugial and recolonization zones for this species i ndicate that more than one refugial region contributed to northern recoloni zation. Haplotypic diversities in recolonized regions are greatest in south -central populations (i.e., southern Great Lakes region), while only one ha plotype (haplotype 1) predominates in northern, western, and eastern postgl acial zones. Large phylogenetic differences were found between northern and southern populations. Populations outside the zone of glaciation were the most genetically heterogeneous and were represented by fish from all six (A -F) of the major evolutionary clades identified. Only fish from the A, B, a nd C clades were found in glaciated regions, with C lineage fish restricted to south-central glaciation zones. Fish from the C clade are putatively th e most ancestral lineage within the species based upon composite shared RFL Ps with lake trout (Salvelinus namaycush) and Arctic char (Salvelinus alpin us).