Graduate Program

Biological Sciences and Sustainable Energy (dual degree)

Degree Name

Master of Science (MS)

Semester of Degree Completion

Summer 2025

Thesis Director

Eden Effert-Fanta

Thesis Committee Member

Eloy Martinez

Thesis Committee Member

Thomas Canam

Abstract

Freshwater systems are affected by current climate extremes, forcing species found in these systems to withstand drastic changes in temperature. Temperature changes affect these organisms by altering their metabolic rate and energy balance. Increases in temperature can lead to an increase in oxygen consumption, which ultimately increases the need for more energy production. Mitochondrial energy transduction of green sunfish (Lepomis cyanellus) and many other fish species after a thermal insult, has hardly been explored. This study complements the limited research available on mitochondrial function in similar species, as they ignore the possibility of consecutive thermal events, which are becoming more common in the present. The objective of this study was to examine L. cyanellus response to temperature, achieved by acclimating specimens to either a constant 30ºC or a variable temperature regime ranging from 19ºC-28ºC on a diurnal basis. Assay temperature 30ºC was chosen as inland aquatic ecosystems have been shown to fluctuate 10ºC daily and nears the thermal maximum of L. cyanellus (Dai et al., 2022). Specimens were acclimated to 20ºC for 30 days to establish a common environment before the experiment. On day 31, experimental groups were subjected to their corresponding thermal regime. During the two weeks of experimentation, fish specimens were subsampled for liver mitochondrial isolation, from day 0, 5, 10, and 15. Purified liver isolation was obtained through homogenization and centrifugation of liver tissue to produce an isolated mitochondrial pellet. Mitochondrial function was assessed using a high-resolution respirometry system, where respiratory states were determined. Oxygen flux was monitored employing a substrate titration protocol at assay temperatures 15 ºC, 25 ºC, 28 ºC, 30 ºC, and 34ºC. Results varied across control specimens, but the variable thermal regime specimens displayed a lower uncoupled respiration, associated with proton conductance across the inner membrane and phosphorylation compared to the constant thermal regime. Respiration uncoupled from ATP production could benefit the cells in reducing oxidative stress, however this benefit also results in reduce efficiency of energy transduction as a tradeoff. Ultimately, energy-intensive processes such as somatic and reproductive growth could be challenged with the acclimation to current and forecasted thermal extremes.

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