| Summary: | Degree: Doctor of Philosophy Abstract: Post-glacial lakes, a common feature in northern landscapes, provide favorable ecosystems for studying intra-specific diversity in fishes. Great Bear Lake, with its large size and virtually pristine, recently colonized cold water habitats, provides unique opportunities for Lake Trout (Salvelinus namaycush) diversification. This thesis presents a new case of exceptional intraspecific diversity of Lake Trout in Great Bear Lake, featuring four co-existing shallow-water morphotypes. In chapter 2, I combined classical morphometric/meristic measures with shape analysis (geometric morphometrics) to quantify morphological differences among adult and juvenile shallow-water Lake Trout. Head and fin measurements best discriminated the adult morphotypes whereas little differentiation was found in body shape. No consistent patterns of variation were found among juveniles, suggesting that divergence develops at later stages. The lack of body shape variation among morphs combined with the size the lake, led me to investigate geographic-based morphological patterns within the five arms of Great Bear Lake in Chapter 3. Within each of the three more common morphotypes, morphological measures, particurlaly body shape differences, were found to vary among lake arms. Genetic and morphological distance matrices were also compared to investigate potential parallel patterns, and suggested observed morphological variation is a phenotypically plastic response to distinct environments. In Chapter 4, I analyzed stomach contents and fatty acids to investigate diet partitioning among the four sympatric shallow-water morphs of Lake Trout as a potential explanatory mechanism for diversification since trophic polymorphism is common among post-glacial fishes. Results suggested that polymorphism in the Lake Trout of Great Bear Lake is partially maintained by diet differences and by some habitat partitioning, but some overlap and seasonality in resource use were also found among morphs in this northern lake. ...
|
|---|