The Influence of Temperature Variability on Metrics of Life History in Brook Trout (Salvelinus fontinalis)
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Increased mean annual temperatures and temperature variability associated with climate change is expected to have detrimental effects on the distribution, growth, survival, and phenology of many commercially and recreationally important cold-water fish. Using a common-garden experiment, we investigated the phenotypically plastic responses of two populations of brook trout (Salvelinus fontinalis) to bidirectional temperature variability. Specifically, we examined the effects of four temperature variability treatments (temperature constancy, periodic variability, low stochasticity, and high stochasticity) on mortality and average total fish length over a 41-day period. Fish populations were then monitored for a subsequent 47 days at a normal, consistent temperature. Trout exposed to the high stochasticity treatment (Treatment 4) consistently experienced the lowest survival and had significantly more deaths than fish in all other treatments in two of the three time- period cycles analysed. Seventeen days following the experiment, the fish exposed to the high stochasticity treatment (Treatment 4) continued to experience significantly more deaths than all the other treatments. While there were no significant differences between treatments observed at the end of the monitoring period, a reversal of the general trends was observed, in which survival was found to decrease with decreasing temperature variability. Trout from the WN population experienced significantly more deaths than the OB population throughout the monitoring period. Average total fish length was significantly higher in the temperature constancy (Treatment 1) and low stochasticity (Treatment 3) treatments than in the periodic variability (Treatment 2) and high stochasticity (Treatment 4) treatments. Trout from the WN population were significantly smaller when compared to the OB population. There was no statistical relationship observed between survival and constancy at any time during the study, while a significant, positive relationship between average total length and constancy was found for the OB population. While a portion of our results could be attributed to issues during the experimental period, our findings generally suggest that high temperature variability has a significant, negative effect on metrics of fitness in brook trout. Additionally, brook trout originating from smaller populations potentially exhibit adaptive plasticity with regards to survival and growth when faced with environmental stressors, such as temperature variability.