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Fluvial mountain whitefish (prosopium williamsoni) in the Upper Fraser River: a morphological, behavioural, and genetic comparison of foraging forms Troffe, Peter M.


Members of the family Coregonidae are notoriously plastic in their morphology and life histories, but in British Columbia there is little evidence of the kind of variation in trophic structures seen elsewhere in North America and Europe. There is, however, one exception — the mountain whitefish, Prosopium williamsoni. Museum, and field collections of fluvial mountain whitefish from the upper Peace, Columbia, and Fraser river systems commonly contain two sympatry phenotypes of fluvial mountain whitefish. One form (the most common) is characterized by a short blunt snout while, the other form has a long slightly upturned snout. I refer to this latter from as the 'pinocchio' form. Individuals with the pinocchio nose are not confined to British Columbia but are also known from isolated populations in Utah, the upper Missouri system, and the Olympic Peninsula in Washington State. The phenotypes from the Upper Fraser system differ in morphological features usually associated with trophic adaptations including gill raker counts and cranial architecture. Furthermore, the forms exhibit different foraging behaviours in sympatry, suggesting they occupy different foraging niches. A mitochondrial DNA survey reveals that pinocchio and normal mountain whitefish from Upper Fraser River tributaries have significantly different haplotype frequency distributions. The nature of the haplotype variation suggests either asymmetrical reproductive isolation — with normal males avoiding pinocchio females — or strong selection against hybrid progeny.

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