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UBC Theses and Dissertations

Physiological trade-offs underlying growth variation from individuals to species : consequences for integrated phenotypic differentiation and ecological diversification in juvenile salmonids Monnet, Gauthier


The purpose of my thesis research was to explore the physiological and behavioural correlates and trade-offs associated with faster growth, and their consequences for phenotypic and ecological differentiation along productivity gradients in salmonids. I examined variation in behavioural, digestive and bioenergetic strategies between different ecotypes and species of wild salmonids that differ in ecological requirements. Juveniles of large-bodied piscivore vs. small-bodied insectivore rainbow trout differed sharply in bioenergetics and behaviour. Relative to insectivore fry, piscivores presented a pattern of faster growth, higher food intake, higher basal metabolism, higher growth efficiency and larger digestive organs, but also more proactive behaviours and greater digestive efficiency (e.g., lower digestive metabolism). Faster piscivore growth was traded-off against lower aerobic scope and presumably against lower survival when facing predators. Piscivore and insectivore integrated phenotypes largely differentiated along the slow-fast continuum of the Pace-Of-Life Syndrome framework (Réale et al., 2010). This result was consistent with specialization of the two ecotypes to rearing habitats that differ in productivity – insectivores occur in tributaries with low prey availability relative to the piscivore rearing environment. The coherence between fast growth and high habitat productivity also emerged as a key driver of the post-emergence dispersal of piscivore fry along a productivity gradient in the Lardeau River. Juvenile steelhead trout and coho salmon also differed in growth and bioenergetics. Relative to coho salmon, faster-growing steelhead trout had higher food consumption and digestive metabolism but lower growth efficiency, which differentiated the two species along an energy-maximizing (steelhead) vs. efficiency-maximizing (coho) continuum (Rosenfeld et al., 2020). This pattern was largely consistent with their specialization to adjacent habitats (pools for coho, riffles for steelhead) along increasing prey flux gradient in coastal streams where the species co-occur. Steelhead trout presented higher aerobic scope than coho salmon, which compensated for their elevated digestive metabolism and ultimately resulted in the convergence of aerobic budgets between the two species. Overall, I demonstrate: i) the existence of multiple sets of physiological trade-offs associated with growth differentiation in salmonids from individuals to populations and species; and ii) the consequences of integrated phenotypic differentiation for ecological specialization along natural productivity gradients.

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