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Lecture 13

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BIOL 370
Dinu Nesan

Lecture 13: Thermoregulation - Thermal physiology is a critical component of animal survival & fitness o Smaller animals are at greater risk o Every animal has a thermotolerant zone - Important macromolecules are especially sensitive to temperature variation o Membrane lipids & enzymes specifically o Certain animals have evolved thermotolerant enzymes - Thermal energy influences chemical interactions (macromolecular structures & biochemical reactions) - Ambient temp (T A: Temperature of surrounding, MOST IMPORTANT environmental influence on the animal’s thermal strategy o Animal must be able to survive thermal extremes & thermal change - Thermal niches o Spatial variation in temperature: Variations across the landscape  TAin alpine regions vary due to altitudinal gradient  Large body of water has varying A due to depth (10:C difference) o Temporal variation in temperature: Variations due to different time  Terrestrial & aquatic environments have relatively constant TA  Polar & temperate environments have seasonal and daily cycles of heat and cold  Air temperatures changes more rapidly than water temperatures (20:C difference) - Sources of energy o Animal is warmed by radiant energy of the sun & those reflected from the surrounding o Animal radiates thermal energy to the surrounding air o Thermal energy are exchanged through objects in contact with external surface  Cooled if thermal energy is conducted away o Movement of air can enhance the efficiency of thermal exchange through convection - Surface Area to volume ratio o The exposed surface area influences all aspects of heat exchange  High ratio (Bigger SA – smaller body size) ↑ rate of heat exchange  Large animals exchange heat more slowly than smaller animals  Lose heat more slowly & retains heat better o Bergmann’s rule: Animals living in cold environments tends to be larger o Allen’s rule: Animals in colder climates have smaller extremities  A+B: Animals @ polar regions are larger with shorter leg than of the same species @ more temperate regions o Body posture can also alter the exposed surface area  Huddling with other animals or reduces behavior etc.  Dogs stretch out when they are hot & rolls up when they are cold  Pythons roll into a ball after meal to conserve metabolic heat  ↓ SA by 85%  Naked mole rates huddle when temperature drops below 22:C - Insulation: Layer of material that reduces thermal exchange (disrupts flow of thermal energy from core to external surface areas) o Internal insulation: Blubber of marine mammals, a thick layer of adipose tissue o External insulation: Hair, Feathers traps the movement of molecules (air & water) between the coat  E.g. cold temperature, bird changes feather orientation to alter the volume of air trapped within the coat o How effective the insulation is depends on its thickness (thicker = more insulated)  Animal at colder environments have thicker coats with greater insulating capacity  The thickness of external insulations can be altered seasonally with low metabolic costs (dead) - Every animal have a thermal strategy (2 major) o Combination of behavioral, biochemical & physiological responses that ensures body temperature (T )B is within an acceptable limit (To control the transfer of energy)  Tolerance: T allowed to vary along with T B A  Regulation: TBdoesn’t vary with TA o Thermal strategy based on the relative stability ofBT  Poikilotherm: TBvaries in response to TA  Homeotherm: T doBsn’t vary, remains stable  Depends on the environment: If an ectotherm is transferred to a controlled environment, it’s a homeotherm because there’s no variations in T A if transferred outside, it is a poikilotherm when theAT changes o Thermal strategy based on the source of thermal energy (T ) A  Ectotherm: T Aetermines T B  Endotherm: Internal heat is generated to maintain T Begardless of TA o Temporal Heterotherm: T changes over time B  E.g. Hibernating animals (B decreases during winter)  Endotherm, done to conserve energy in cold temperatures  E.g. Pythons after a meal rolls into a ball  Ectotherm, most ectotherm rapidly loses metabolic heat, done to speed up digestion & nutrient assimilation  E.g. To save metabolic energy, birds decreases core B in response to low A during nighttime o Regional Heterotherm: T vBries in different regions of the body  E.g. Billfish are ectotherm with heater organs close to the eyes  produce heat near optic nerve to improve visual clarity at deep waters  E.g. Tuna retains myogenic heat in red muscles to increase metabolic activity & contraction  E.g. Insects conserves metabolic heat @ flight muscles before flight to warm up the thorax where the rest of body temperature remains ambient - Thermal Zones of Homeotherms (Stable T ) B o Thermoneutral zone: Range of temperature optimal for physiological processes, range of minimal metabolic rate (range of tolerable T varies depending on the species) A o Upper critical temperature (UCT): High temperature where metabolic rate increases as the animal induces a physiological response to PREVENT OVERHEATING  When above, there’s onset of hyperthermia o Lower critical temperature (LCT): Low temperature where metabolic rate increases as the animal induces a physiological response to INCREASE HEAT PRODUCTION  When under, there’s onset of hypothermia - Thermal tolerance of Poikilotherms (Variable T B o No thermoneural zone, upper critical temperature or lower critical temperature o Preferred temperature: T Aor optimal physiological functions o Incipient lethal temperature: A where 50% of animals dies  Incipient upper lethal temperature  Incipient lower lethal temperature  Middle: Preferred temperature “range of tolerance” - Thermal tolerance ability of Poikilotherms & Homeotherms o Eurytherm: Tolerate wide range of T AIf homeotherms, has wide thermoneutral zone, if poikilotherms, has large range of tolerance polygon area)  Can occupy a greater number of thermal niches than stenotherm (better than competitor) o Stenotherm: Tolerate narrow range of T A - Structures of macromolecules under temperature variation o 4 classes, proteins & lipids are mostly affected by temperature over normal rage  Hydrogen bonds & van der Walls forces are disrupted by high temperature  Hydrophobic interactions are stabilized at high temperature  The effects of temperature is relative to the importance of each type of bond o E.g. Membrane structure  Cold temperature: Solidify of phospholipids which impairs protein movement  Hot temperature: Liquefy of phospholipids which compromises the integrity & decreases the effectiveness of the membrane as a barrier - Temperature vs. Enzymes o Temperature affects the rates of processes, the conformation, and enzyme-substrate binding affinity o The functional properties of enzymes depends on the prevailing temperature  E.g. In Goby fish, increase in temperature is proportional to decrease in affinity o All species have approximately the same enzyme-substrate affinity @ respective B  Species with different body temperatures have different molecular forms  E.g. Lactate dehydrogenase (LDH) from muscle cells  Within the same genus, there are different forms of LDH proteins, all with similar enzyme-LDH affinity  The amount of LDH can be changed but not the type of LDH “Quantitative adaptation” o The affinity of certain enzyme is far more sensitive to changes in temperature in certain species than in others  E.g. AchE in Antarctic fish (lives @ -1.96:C) is far more sensitive to temperature variations than AchE in mullet - Adaptations to thermal variations o Ectotherms can remodel their tissues “thermal acclimation” in response to long-term changes in temperature  Quantitative strategy: Increase the # of the same type of metabolic machinery  E.g. Increase the # of muscle mitochondria in lo
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