Thermal relations (Chapters 9 and 10) 

I.        Heat transfer between animals and their environments  207

          A.  Determinants of body heat and temperature:  Heat production-

          1.  Behavioral mechanism

          2.  Autonomic mechanisms- accelerated metabolism of energy reserves

          3.  Adaptive mechanisms- acclimatization     

          B.  Heat transfer- rate of heat transfer in and out of an animal depends on 3 factors 

          1.  Surface area- small animals- high heat flux per unit of body weight

          2.  Temperature difference- body temp. and ambient temp. Ta-Tb

3.      Special heat conductance of the animal's surface 

          C.  All organism exchanges heat with its environment by 4 physical processes:  209      

          1.  Conduction- direct transfer of thermal motion (heat) between molecules of environment and body surface

                   water is 50-100X more effective

2.  Convection- mass flow of air or liquid past the body surface-

    as breeze contribute to heat loss; wind-chill factor contribute to harshness of Ta

3.  Radiation- emission of electromagnetic waves produced by all objects warmer than absolute zero. 

 Heat transfer between objects that are not in direct contact,

                    e.g. animals absorb heat radiating from the sun.

                          Polar bears and arctic seals- fur clear, not white; each hair functions like an optical fiber-

                               transmits UV radiation to the black skin, where energy is absorbed and converted to body heat

4.  Evaporation- loss of heat from the surface of a liquid that is losing some of its molecules as gas  

 

 

II. Thermal tolerance- thermal neutral zone, lower and upper critical temp

          A.  Phylogenetic differences in thermal tolerance- reflected in their geographical distributions

                   e.g. temp tolerance and breeding time in 4 species of frogs 

          B.  Seasonal changes in thermal tolerance- photoperiod

                   Long photoperiod (summer) - increase resistance to heat;

                   winter- short photoperiod- increase tolerance to cold

                   E.g. catfish has an upper lethal temp of 36C during summer

                             This fish will die when temp exceeds 28C during winter

                             The lethal temp changes with the season.

          C.  Limits of temp tolerance- modified by previous thermal history

                   E.g. goldfish - wide temp tolerance 

          D.  Oxygen plays an important role in speed of adaptation

                   (age, size and quality of water also affect tolerance)

          E.  To compensate for temp change- metabolic rate changes

                   E.g. sand crab- at 3C, winter animals consume O2 @

                             a rate 4X that of summer animals @ the same temperature  

 

 

III. Temperature classifications of animals- base on main source of body heat 209

          A.  Poikilotherms- ectodermic; depend on ambient source of heat;

                 invertebrates, fishes, amphibians, reptiles

          1.  Heat exchange with environment more important

2.  Low rate of metabolic heat production

          3.  High thermal conductivity- poorly insulated

          4.  Behavioral temp. regulation-the only type of thermoregulation

5.  Adaptation to cold environment: freeze tolerant vs. freeze intolerant (animals die if any internal ice formation)

a. Solutes lower the freezing pt. and extent of supercooling (lowering freezing pt of H2O- 0oC)

b. Glycerol- high conc. in overwintering insects- increase cold tolerance- extreme supercooling                 

                              i. Lower supercooling pt., avoid ice crystal formation

ii.       Protective action against freezing damage once ice formation takes place  

iii. Example: glycerol protects rbc and spermatozoan 

                   c.  Antifreeze substance in blood and tissue of fish- glycoprotein-

                        acts by preventing the addition of water molecules to the crystal lattice of ice          

                   d.  Freeze-tolerant animals- e.g. intertidal areas survive extensive ice

                              formation within their bodies

                              i.  Nucleating agent (a protein)-aids in ice formation; found in hemolymph                            

                              ii.  Increase in blood glucose level in response to beginning ice

                                  formation- increasing tolerance

                   e. Shivering or ordinary muscle contraction

                   f. Change in blood flow to skin 

          B.  Homeotherms- endothermic; animals generate heat on their own

          1.  Land mammals maintain a relatively constant Tb

          2.  Physiological and behavioral adjustments:

a. Changing the rate of metabolic heat production-

     Example:  when exposed to cold-metabolic heat production - 2X or 3X through increase activity of skeletal muscle,

      and nonshivering thermogenesis (hormonal, brown fat- specialized for rapid heat production) 

                        i. High MR - must take in large quantity of food and water

                        ii. Surface area to volume ratio- small animals lose heat faster

iii. Large quantity of energy used to maintain body temp. -

small % for growth and reproductions 

                        b. Adjusting the rate of heat exchange between an animal and its environment - vasodilation/vasoconstriction,

                                           e.g.  Blood flow to rabbit's ears decreases when cold; hair is also important in regulating heat exchange

                                         Counter current heat exchange permits selective restriction of heat flow to appendages

c.     Cooling by evaporative heat loss- evaporation from the respiratory tract can be increased by panting,

                  via the skin by sweating; some rodents (no sweat glands); spread saliva on their heads  

d.  Bats use saliva and urine to cool themselves by evaporation 

e.  Behavioral responses- relocating; bask in the sun in winter, find cool and damp areas or burrow in summer. 

 

IV. Ectothermy 198

          A.  Three responses:  Acute and chronic responses, evolutionary changes

          B.  High temperature-- heat-shocked protein 209

          C.  Freezing temperature 210

 

V.  Homeothermy in mammals and birds 214

          A.  MR increases in both cold and hot environments

          B.  Metabolism-temperature curve

          C.  Insulation- modulated by adjustments of pelage,  plumage, blood flow, and posture

          D.  Shivering and non-shivering thermogenesis 220

          E.  Counter-current heat exchange

          F.  Mammals and birds in hot environments 224

          G.  Mammals and birds acclimatized to winter and summer 227

          H.  Hibernation, torpor, or related processes

          I.  Hibernation as a winter strategy 249

 

VI. Temperature acclimation - multifaceted 

          A.  Cells may increase the production of certain enzymes;

                   compensate for the lowered activity of enzymes

          B.  Cells may produce variants of enzymes that have the same function but different temp. optima 

          C.  Membranes may also change in the proportions of saturated and unsaturated lipids - help keep membranes

                   fluid at different temperatures 

VII. The effects of body size on mammals’ lives in cold environments 248