Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2022

Thesis Director

Eloy Martinez

Thesis Committee Member

Antony O. Oluoch

Thesis Committee Member

Eden L. Effert-Fanta

Abstract

Environmental factors such as temperature are substantial determinants of the spongy moth, L. dispar, distribution, reproduction, and growth. Accumulating energy reserves at the larval stage is particularly important to L. dispar, since the larvae metamorphose into a fully-grown, non-feeding adult. As non-feeding adults, the energy balance of the pupae must be adequate, to ensure enough energy reserves for adult dispersal, egg maturation and overall persistence of the species in the region. At this stage, environmental temperature also determines daily metabolic demands, and the overall cost of sustaining ecologically relevant activities. Various hypotheses describing a mismatched growth and metabolic rate at supraoptimal temperatures exist, with very few providing a mechanistic explanation of why growth decrease at supraoptimal temperature, while metabolic rate continues to rise on many ectotherms, including insect larval stages. Frequently, studies have shown positive and causative relationships between metabolism and growth suggesting that metabolism drives L. dispar and more broadly, ectotherms, performance. Such as relationship was integrated recently to mitochondrial energy transduction efficiency (METE), which is known to be thermosensitive. Current evidence suggest that mitochondrial METE may be pivotal in whole organismal thermal performance, and our study addresses such knowledge gap in the L. dispar. Post-diapause egg masses from a captive breeding population were manually disrupted and eggs were pooled. Subsamples of eggs were distributed in hatch-out containers at the corresponding acclimation temperatures. Acclimation setup consisted in two temperature treatments, 20°C and 30°C, each with a controlled with a photoperiod of 14L:10D. To assess the thermal sensitivity of mitochondria, we used a high-resolution respirometry system. Gut mitochondria were isolated and the performance of the electron transport system (ETS) was evaluated under multiple substrates. Proton conductance across the inner membrane (LEAK) did not differ between acclimation groups, with the exception of LEAK flux under complex Iactivating substrates at 15°C. Mitochondrial oxygen flux linked to LEAK increased with assay temperature. Oxygen flux associated with LEAK also show an additive effect; the activation of additional electron carriers in the ETS increased the overall electron transfer capacity of the ETS, increasing the LEAK rates observed. Oxygen flux associated with oxidative phosphorylation (OXPHOS) displayed an increasing trend with assay temperature. Respiratory control ratios (RCR) were calculated from OXPHOS/LEAK significantly decreased in a bi-phasic fashion; lowest rate of change between 15-25°C, and a faster rate of change between 25-34°C. Results from this study show a reduction in METE with increasing temperatures, and aligns with the range thermal insensitivity described for the species in previous studies. Consequently, it is plausible that reductions in developmental performance (both time and rate) can be attributed to changes in METE. Both metabolism and development are energetically expensive, and as such influenced by the METE. Moreover, the lack of variation in RCR between acclimation groups in this study suggests that the bioenergetic machinery of L. dispar mitochondria adapts rapidly under short term acclimation (via regulatory processes controlling the ETS electron carrying capacity), and that adaptive changes in this fast-growing stage are beneficial to sustain energy-dependent processes at rapidly changing environmental temperatures.

Available for download on Friday, May 12, 2023

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