Abstract

Maintaining population diversity is important for species survival and fisheries productivity. Research on several large lakes has documented the presence of multiple genetically- and morphologically-distinct populations within harvested fish species but less is known of population structuring in pristine lakes. I characterized population structuring of lake trout throughout Mistassini Lake, Quebec (2,335km2), using data from nineteen microsatellite DNA loci, spatial habitat use, morphology and local Cree traditional knowledge. I found that the lake is home to a minimum of five populations. These exhibit low to modest levels of genetic differentiation, partial spatial segregation by depth and basin, indiscriminate body and head morphologies, but remarkable within-population variation in morphology. The relationship between genetic and ecological differentiation was inconsistent across ecological metrics assessed, and traditional knowledge recognized attributes of some, but not all of the demarcated populations. Adopting the conceptual framework of ecological speciation as a continuum, I contend that the higher apparent level of within-population phenotypic variation in lake trout relative to other previously studied fish species may explain their lower level of population differentiation, despite their use of numerous distinct habitat niches. I discuss how identifying and recognizing multiple forms in such a pristine boreal lake system, both with western and traditional knowledge, has implications for a better understanding of population diversity and conservation in lake trout and related species elsewhere.