MULTIPLE MODES OF SPECIATION INVOLVED IN THE PARALLEL EVOLUTION OF SYMPATRIC MORPHOTYPES OF LAKE WHITEFISH (COREGONUS CLUPEAFORMIS, SALMONIDAE).

We performed a phylogenetic analysis of mtDNA variation among seven sympatric pairs of dwarf and normal morphotypes of whitefish from northern Québec and the St. John River drainage to address three questions relevant to understanding their radiation. Are all sympatric pairs reproductively isolated? Do phylogenetic analyses confirm that sympatric whitefish morphotypes found in eastern North America represent the outcome of polyphyletic evolutionary events? If so, did all sympatric pairs from the St. John River drainage originate from the same scenario of allopatric divergence and secondary contact? The hypothesis of genetic differentiation was supported for all sympatric pairs from the St. John River drainage, whereas lack of mtDNA diversity precluded any test of reproductive isolation for northern Québec populations. Patterns of mtDNA variation confirmed that dwarf and normal morphotypes evolved in parallel among independent, yet closely related, lineages, thus providing indirect evidence for the role of natural selection in promoting phenotypic radiation in whitefish. Patterns of mtDNA diversity among sympatric pairs of the St. John River indicated a complex picture of whitefish evolution that implied sympatric divergence and multiple allopatric divergence/secondary contact events on a small geographic scale. These results suggests that ecological opportunities, namely trophic niche availability, may promote population divergence in whitefish. © 1997 The Society for the Study of Evolution.