chapter  8
Chapter 8Thermal Stress
Pages 32

Most Œshes, with the exception of a few large pelagic Œsh (e.g., tuna, mako sharks), cannot generate and retain sufŒcient endogenous heat to maintain abody temperature different from that of their external environment because of rapid heat exchange across the gills and the body surface (Hazel and Prosser, 1974; Stevens and Sutterlin, 1976). Thus, as has long been recognized (Glaser, 1929; Fry and Hart, 1948; Fry, 1958), temperature is one of the critical abiotic factors that affect Œshes. Temperature directly impacts the rate of chemical reactions and the stability of weak chemical bonds, profoundly affecting the function of proteins and biological membranes (Schulte, 2011). Low temperatures tend to stabilize weak chemical bonds (including hydrogen bonds, ionic bonds, and hydrophobic interactions) while high temperatures tend to destabilize them. The properties of biological membranes also depend on these interactions. For example, biological membranes will tend to be more «uid at high temperatures and less «uid at low temperatures, which affects the permeability of these membranes and the functional properties of the proteins embedded within them. Similarly, high temperatures destabilize the bonds that support the secondary, tertiary, and quaternary structures of proteins, resulting in gradually increasing «exibility, which ultimately

8.1 Introduction .......................................................................................................................... 257 8.1.1 Characterizing the Effects of Temperature .............................................................. 258 8.1.2Anthropogenic Thermal Stress .................................................................................260 8.1.3Behavioral Responses to Temperature...................................................................... 261 8.1.4Time Scales of Responses to Thermal Stress ........................................................... 262

8.2 Responses to Acute Thermal Stress ..................................................................................... 262 8.2.1 Cellular Stress Response to Acute Thermal Stress .................................................. 263 8.2.2Effects of Behavior on the Cellular Stress Response ...............................................265 8.2.3Metabolic Responses to Acute Thermal Stress ........................................................265 8.2.4Cardiorespiratory Responses to Acute Thermal Stress ............................................266 8.2.5 Effects of Acute Temperature Exposure on Swimming Performance ..................... 267

8.3 Acclimation and Acclimatization to Thermal Stress ...........................................................268 8.3.1Acclimation at the Molecular and Cellular Levels ...................................................268 8.3.2Acclimation of the Cellular Stress Response ........................................................... 270 8.3.3Molecular and Cellular Responses to Low Temperature Acclimation ..................... 271 8.3.4 Tissue and Organismal Acclimation Responses ....................................................... 273

8.4 Epigenetic Effects in Response to Temperature ................................................................... 274 8.5Adaptation to Thermal Stress ............................................................................................... 275

8.5.1Adaptation to Constant Cold .................................................................................... 277 8.6Conclusions and Perspectives ............................................................................................... 278 Acknowledgments .......................................................................................................................... 279 References ...................................................................................................................................... 279

culminates in protein denaturation at high temperatures. In contrast, at low temperatures, proteins become less «exible, which can impede their biological function by reducing their ability to undergo the changes in conformation required to bind with substrates and catalyze reactions. Thus, biochemically catalyzed reactions tend to proceed more slowly atlow temperatures and more quickly athigher temperatures, up to the point where the proteins begin to denature, atwhich point reaction rate decreases rapidly. In addition, temperature directly affects reaction rates by changing the thermal energy in the system. At higher temperatures, molecules move more swiftly and with higher energy, and are therefore more likely to undergo the high-energy molecular collisions that are required to overcome the activation energy barrier of the reaction. Together, the direct effects of temperature on reaction rates and on the stability of weak bonds result in an increase in reaction rates with temperature up to the point that proteins begin to denature or membranes become too «uid to function effectively. As most biological processes depend upon the proper functioning of proteins and membranes, these effects on protein «exibility, membrane «uidity, and reaction rate are integrated across all levels of biological organization to affect processes from the level of individualbiochemical reactions up to population growth rates and ecosystem processes (Kingsolver, 2009). In this chapter, we review the short-and long-term effects on Œshes due to both rapid and prolonged exposure to temperature change and how these effects may be interpreted as stressful.