Gill morphology as an indicator of thermal adaptation and phenotypic plasticity in Atlantic salmon (Salmo salar)

Power Smith, Isaiah (2023) Gill morphology as an indicator of thermal adaptation and phenotypic plasticity in Atlantic salmon (Salmo salar). Memorial University of Newfoundland, Memorial University of Newfoundland. (Unpublished)

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Abstract

Climate change is a growing problem facing freshwater ecosystems, as water conditions continue to fluctuate with increasing intensity, and this is having major impacts on the biodiversity of these habitats. For many fish species, including Atlantic salmon (Salmo salar), adaptations to this environmental variability will be critical to their long-term outlook. This study explores how Atlantic salmon may respond to climate change and whether there is evidence that they can adapt to warming water conditions. To accomplish this, I examined whether gill morphometrics are an indicator of thermal tolerance in Atlantic salmon. Two potential drivers of thermal tolerance were assessed: thermal adaptation and phenotypic plasticity. Thermal adaptation is driven by genetic responses to the environment, which may evolve over generations, while phenotypic plasticity can occur over a much shorter period of time (i.e. within an individual's life span). Using three geographically separate populations that span a thermal gradient, Atlantic salmon gill metrics were compared and related to CTmax data to thereby assess thermal adaptation. To assess phenotypic plasticity, gills from one population were compared before and after exposure to prolonged warm temperatures. We found no significant evidence of thermal adaptation in gill morphology between populations and no relationship between CTmax temperatures and gill morphology, as well as no evidence of any phenotypic plasticity occurring over the course of our experimental temperature challenge. However, there were plenty of interesting trends in the data which will be discussed in depth later in this thesis. Overall, this study serves to help predict both future population-level and individual-level responses to climate change in Atlantic salmon in Newfoundland.

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