Integrative Investigation of the Physiological Mechanisms That Contribute to Freeze Tolerance in Cope’s Gray Treefrog Dryophytes chrysoscelis
Date of Award
5-5-2024
Degree Name
Ph.D. in Biology
Department
Department of Biology
Advisor/Chair
Carissa Krane
Abstract
Vertebrate freeze tolerance is an extraordinary phenomenon in which up to 70% of an animal’s extracellular fluids are converted to ice while circulation, respiration, and neuronal function are all simultaneously suspended during freezing. Upon thawing, animals must tolerate the resumption of physiological function, restore intracellular fluid volumes, and repair injuries that occurred during freeze-thaw. The mechanisms that enable animal freeze tolerance vary by species and represent a myriad of biochemical, cellular, systems, and organismal strategies. Cope’s gray treefrog Dryophytes (Hyla) chrysoscelis is a freeze tolerant anuran that repeatedly freezes and thaws each winter in part by utilizing a complex system of cryoprotectants including glycerol, glucose, and urea. Intracellular transport is facilitated by specialized aquaglyceroporin proteins that enable transmembrane movement of water and the cryoprotectants glycerol and urea during freeze-thaw. The physiological mechanisms that enable freeze tolerance in D. chrysoscelis are not entirely understood and cannot be explained by cryoprotectant accumulation alone. The aim of this dissertation is to explore the unknown physiological mechanisms of freeze tolerance in D. chrysoscelis by using an integrative perspective that incorporates all levels of biological organization. Novel experimental protocols were used to evaluate the ecophysiological effects of repeated freezing and thawing, characterize organismal responses to seasonal and cold acclimation, and determine the effects of cold acclimation and freeze-thaw cycles on membrane lipid composition using 1H-NMR analysis. The results from these studies emphasized the complexity of freeze tolerance in D. chrysoscelis and revealed several novel aspects of freeze tolerance in this species including dynamic blue and green dorsal coloration in frozen and thawing frogs, “freeze resistance” in a freeze tolerant vertebrate, evidence of seasonal acclimation, membrane lipid remodeling, and remarkable physiological plasticity in response to repeated freezing and thawing. These findings meaningfully advance the fields of comparative physiology, cryobiology, and ecophysiology and provide important insights into the physiological mechanisms that enable vertebrate freeze tolerance. The broader implications of this work may also enhance biomedical applications in freeze tolerance and cold storage of human cells and tissues required for tissue banking and organ transplantation.
Keywords
freeze tolerance, physiology, integrative physiology, comparative physiology, cold acclimation, seasonal acclimation, lab acclimation, repeated freeze-thaw, repeated freezing and thawing, cryoprotectants, lipid composition, treefrog, cold tolerance, behavior, morphology, color change, freeze resistance
Rights Statement
Copyright 2024, author
Recommended Citation
Yokum, Elizabeth, "Integrative Investigation of the Physiological Mechanisms That Contribute to Freeze Tolerance in Cope’s Gray Treefrog Dryophytes chrysoscelis" (2024). Graduate Theses and Dissertations. 7615.
https://ecommons.udayton.edu/graduate_theses/7615
