Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2020

Thesis Director

Eloy Martinez

Thesis Committee Member

Michael A. Menze

Thesis Committee Member

Thomas Canam


As average global temperature increase, the frequency and magnitude of extreme temperatures in shallow aquatic ecosystems are more ubiquitous. In order to understand how these changing thermal regimes affect aquatic ectotherms, it is essential to develop studies evaluating the response of ectotherms to seasonal fluctuating thermal regimes. Previous studies on fluctuating temperature regimes have reported an increased physiological stress leading to morphological, behavioral and biochemical adaptations. From the latter, the adaptive capacity and seasonal performance associated with optimal function of the oxidative phosphorylation system (OXPHOS) are key for species persistence. However, studies on this matter are scarce. This study explores the seasonal changes and thermal sensitivity of the OXPHOS system in liver mitochondria of the bluegill sunfish species Lepomis macrochirus, inhabiting a shallow riverine system. Our study on liver mitochondria from L. macrochirus show significantly higher uncoupled proton conductance (LEAK) and cytochrome c oxidase (COX) activity in individuals captured in the fall compared to specimens investigated in summer and spring seasons. Flux control ratios such as coupling control ratio (CCR) and respiratory control ratio (RCR) were significantly reduced in the fall compared to warm-acclimated individuals in the summer and spring. These findings suggest that mechanisms regulating COX activity are in place to fine-tune mitochondrial function, and consequentially increase fitness in ectotherms inhabiting shallow, aquatic habitats with highly fluctuating temperatures.