DOI

https://doi.org/10.25772/3K1A-4055

Author ORCID Identifier

https://orcid.org/0000-0002-9844-8203

Defense Date

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Integrative Life Sciences

First Advisor

Salvatore Agosta

Second Advisor

Andrew Eckert

Third Advisor

James Vonesh

Fourth Advisor

Kristine Grayson

Fifth Advisor

Eloy Martinez

Abstract

Climate is a primary factor influencing species range dynamics, particularly for ectotherms whose body temperature is closely tied to the surrounding conditions. While range shifts of ectotherms are attributed to climate warming, the mechanism driving these shifts are not well understood. Studies in macrophysiology demonstrate that the interaction of climate with thermal physiology plays a key role in determining large-scale spatial and temporal patterns for many temperature-sensitive physiological traits. This work has revealed a clear relationship between thermal tolerance breadth and range size. However, more recent analyses of this relationship demonstrate that thermal tolerance breadth only provides a partial explanation for patterns in range size. Resting metabolism is a trait closely tied to energy balance, a key determinant of species distribution and abundance. At the whole-organism level, resting metabolism represents the energetic cost to fuel the maintenance of biological processes. Variation in this trait is related to climate and has a significant impact on how energy is allocated towards growth and reproduction. The aim of this dissertation was to understand the impact of climate on thermal physiology and species range dynamics using the Spongy moth (Lymantria dispar dispar) as a model system. The chapters of this dissertation addressed three primary questions: (Chapter 1) Do metabolic rate-temperature relationships (MR-T) vary across the invasive Spongy moth range and is that variation related to climate? (Chapter 2) How does MR-T vary with ontogeny? (Chapter 3) How does thermal performance at the cellular level compare to whole-organism performance? In the first chapter, we found that MR-T of third instar Spongy moth larvae showed significant variation among wild populations and this variation followed a latitudinal cline that was significantly related to climate variation. In the second chapter, larval MR-T showed significant variation across the first five instars of the larval stage. However, we found that the third instar was the most temperature-sensitive and showed the largest increase in metabolic rate after accounting for differences in body size among instars. In the third chapter, we found that whole-organism performance of metabolic rate and growth were mismatched at temperatures beyond the thermal optimum for growth and development of Spongy moth larvae. As temperature increased, metabolic rate continued to increase while growth rapidly declined. However, mitochondrial performance matched growth performance at these supraoptimal temperatures. Furthermore, this response of MR-T, growth, and mitochondrial performance was consistent across five Spongy moth populations. These results produced three primary conclusions. First, the latitudinal variation in whole-organism MR-T among Spongy moth populations was consistent with a pattern of thermal adaptation to divergent climates and suggests that Spongy moth populations have evolved in response to climate as they have spread and expanded their invasive range. Second, the thermal physiology of Spongy moth show significant variation during ontogeny. However, while MR-T does change with instar, our findings suggest it would not alter the conclusions of chapter 1 which is based on the third instar. Finally, the mismatch of MR-T with growth and mitochondrial performance follows the predictions made by the mitochondrial efficiency hypothesis which posits that changes in mitochondrial coupling efficiency is a key mechanism for reducing ectotherm performance. These provide strong evidence for a temperature-dependent link between mitochondria and whole-organism performance. The implications of these findings for the Spongy moth invasion, species range dynamics, and ectotherm performance are discussed further in each chapter.

Rights

© Sean D. Powers

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

12-15-2023

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