Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Fall 2022

Thesis Director

Eloy Martinez

Thesis Committee Member

Eden L. Effert-Fanta

Thesis Committee Member

Robert E. Colombo

Abstract

Black Crappie Pomoxis nigromaculatus and Bluegill Lepomis macrochirus are popular sportfishes that co-occur in similar bodies of water throughout most of the Central and Eastern United States but have distinct thermal physiologies. L. macrochirus is often found in warmer regions of freshwater reservoirs, where P. nigromaculatus tends to exploit cooler regions, especially in power plant cooling reservoirs. The coal-fired Coffeen Power Station ceased energy production in October 2019, providing an ideal scenario to study the organismal effects of the sudden shift in thermal regime. Previous studies showed that P. nigromaculatus inhabited the less thermally-impacted areas of Coffeen Lake, whereas L. macrochirus were more broadly distributed across the lake. I hypothesized that more thermosensitive species (P. nigromaculatus) will be also reflected at the mitochondrial level, indicated by the properties of the energy transduction (how much oxygen and carbon substrates are coupled to ATP production) machinery. Both water quality and specimens were monitored between the fall of 2019 and the fall of 2020, with the objectives of assessing population structure, growth, and subcellular energetics, while simultaneously linking these traits to the changes in physicochemical properties of the reservoir after the thermal shutoff. Following the shutoff of thermal effluent in October of 2019, no values indicating unnatural stratification in the water column were observed. At the population and individual levels, this study found significant differences in organismal growth, with L. macrochirus displaying irregular, linear growth and were unable to have von Bertalanffy functions fit to them. Linear regressions run on fall 2019 Bluegill, spring 2020 Bluegill, and fall 2020 Bluegill showed r2 values of 0.9845, 0.9961, and 0.9789 respectively, indicating a very high degree of fit to the data. Despite P. nigromaculatus and L. macrochirus seasonal fall data showing a statistically significant difference in distributions for length frequencies when v compared using a Kolmogorov-Smirnov test (p < 0.05), both species displayed similar patterns in mortality. Total annual mortality values for fall Black Crappie, spring Bluegill, and fall Bluegill were 0.606, 0.774, and 0.732 respectively. When testing homogeneity of regression slopes on their respective catch curves, both species linear regressions for seasonal mortality proved to be similar to one another (p > 0.05). At the subcellular levels, this study found significant differences in mitochondrial function between species, assay temperatures, and seasons. Fall 2019 samples at 30˚C showed coupling ratios of ATP production divided by the Electron Transport System (ETS) capacity (P/E) of 0.96 for P. nigromaculatus, compared to 0.84 for L. macrochirus. Fall 2020 runs showed very similar significant findings, with noticeable interspecies differences in coupling efficiency and proton leakage also documented. These results show the Oxidative Phosphorylation System (OXPHOS) of P. nigromaculatus operating closer to the ETS capacity in vitro, compared to L. macrochirus. Interestingly, L. macrochirus mitochondria showed less coupling, indicating the species function less efficiently under a wider range of temperatures. Complex I OXPHOS during fall 2019 showed increased activity for Black Crappie (295.766 ± 69.241) when compared with Bluegill (79.616 ± 59.965; Two-way ANOVA, df = 17, p = 0.033). This increase in Complex I activity for Black Crappie could further solidify their energetic machinery as a mechanism for temperature tolerance, as this protein is known for its heightened sensitivity to temperature change. Results suggests that the lower occurrence of P. nigromaculatus in previously warmed sectors of the reservoir may be a consequence of the thermal sensitivity at the mitochondrial level.

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