How Life-History Variations Are Linked to a Polymorphic Case of Four Shallow-Water of Lake Trout from Great Bear Lake, NT?

Phenotypic variation within populations is common in many species of salmonids, especially when inhabiting northern postglacial systems. We compared the life-history attributes among four Lake Trout morphs co-existing in the shallow-waters of Great Bear Lake, NWT, Canada. Adult growth rate, age- and size-at-maturity, and survival differed among morphs, consistent with their degree of foraging specialization and predictions from foraging theory, e.g., reduced somatic growth and higher investment in reproduction in the generalist morph, high growth throughout life in the piscivorous morph, and intermediate life-histories in the more benthic- and pelagic-oriented morphs. However unexpected findings also arose, reflecting the complexity of this system, such as comparable immature growth rates among morphs. Other traits, such as the high proportion of resting individuals among all morphs, suggest life-history adaptations to northern latitudes. Fecundity and egg size also varied among morphs. Overall, Lake Trout from Great Bear Lake demonstrated remarkable longevity and exceptional asymptotic sizes, even for a northern freshwater ecosystem. Our study of polymorphic Lake Trout provides insights into life-history evolution among morphs that use different food sources and habitats, and contributes to our understanding this lake ecosystem that exhibits one of the highest recorded levels of intraspecific diversity among freshwater fish.