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In the face of a changing climate, questions regarding sub-lethal effects of elevated habitat temperature on the physiology of ectotherms remain unanswered. In particular, long-term responses of ectotherms to the warming trend in tropical regions are unknown and significantly understudied due primarily to the difficulties in specimen and community traceability. In freshwater lakes employed as cooling reservoirs for power plants, increased physiological stress from high water temperature can lead to an increase in mortality, reduce growth, and potentially alter the community structure of fishes. Throughout this study, we employ this highly tractable system to assess how elevated thermal regimes can alter the physiology and consequently the ecology of aquatic species. We documented a significantly reduced lifespan, growth performance, and a shift in the age structure toward younger individuals in the thermally impacted population of bluegill (Lepomis macrochirus) in Coffeen Lake in Illinois, compared to a non-impacted control group (Lake Mattoon). Average age calculated for the Lake Mattoon population was 2.42 years, whereas the average age of bluegill from Coffeen Lake was only 0.96 years. The average specimen mass in Lake Mattoon was more than six times that of Coffeen Lake average (Mattoon = 60.26 g; Coffeen = 9.42 g). During laboratory cross-acclimation studies of bluegill from Lake Mattoon at 17.5 and 35.0 °C, citrate synthase activity obtained from white muscle was regulated through acclimation, whereas cold-acclimated specimens exhibited twice the activity at 25 °C, if compared to CS activity values from warm-acclimated specimens. This study raises the questions about the causal relationships between physiological performance and habitat temperature, in particular how thresholds in an organism's physiology may modulate their community structure, and consequently their ecological success.


Final version available at doi:10.1016/j.cbpa.2015.07.014

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