Intraspecific variation in metabolic responses of a cool water fish to increasing temperatures

Growing impacts of climate change necessitate predicting species' vulnerability to altered ecosystems. Assessing vulnerability requires understanding how species' physiology, life history, and ecology vary among populations and can be altered by behavioral, plastic, and evolutionary adaptations. To examine intraspecific variation in sensitivity to climate change, we measured metabolic responses to acute and chronic temperature exposures in three rearing pond populations of walleye (Sander vitreus), a cool-water-adapted fish species threatened by climate change. We show significant differences among rearing pond populations in response to increasing temperatures which may originate from broodstock, developmental plasticity, and acclimation. Our results indicate northern walleye may be more tolerant of acute and chronic exposure to higher temperatures by being able to maintain a higher aerobic scope than more southern populations. Furthermore, even over small geographic distances, populations can have significantly different physiological responses to environmental stressors. Quantifying variation in population-specific metabolic responses can inform predictions of growth, reproduction, and fitness across a species range and clarify the importance of within-species diversity in determining vulnerability to environmental stressors.

Methods
Metabolic rates were collected from walleye (Sander vitreus) using intermittent respirometry utilizing AutoResp v2.3.0 (Loligo Systems, Viborg, Denmark). Raw data was then processed using the FishResp package v.1.0.3 (Morozov et al. 2019) in R-Studio to calculate the standard metabolic rate, maximum metabolic rate, and absolute aerobic scope. Standard metabolic rate was calculated as the average of the lowest 20th percentile of measurements conducted over 16 hours. Maximum metabolic rate was determined to be the highest rate observed across all respiration measurements through a chase routine. Aerobic scope was calculated as the absolute aerobic scope, meaning maximum metabolic rate minus standard metabolic rate. After these calculations metabolic rates were then analyzed following the R-script provided. Additional details pertaining to the methods used for subsequent analysis can be found in the published mansucript.