1. 16-1 D. Thermoregulation 1. Animals show two types of responses to changing environmental temperature

2. 16-2 T B Body Temp. T A Ambient Temp b. Thermoregulator a. Thermoconformer T B will be stable only if T A is constant maintains relatively constant T B

3. 16-3 2. Can classify animals by their source of body heat: a. endotherms: derive heat from internal source b. ectotherms: derive heat from outside sources

4. 16-4 3. Alternatively, animal are classified by stability of heat: a. homeotherms: constant T B over time b. poikilotherms: variable T B over time Does not imply animal has no control Most vertebrates exhibit some degree of control of T B in the wild

5. 16-5 E. Temperature regulation achieved by controlling mechanisms of heat gain and loss Mechanisms of Heat Transfer 1. Conduction Heat gain or loss through direct contact Depends on thermal conductivity of object rate at which heat passes through it

6. 16-6 air: 0.00006 cal/cm 2 sec °C water: 0.00144 cal/cm 2 sec °C Air is good insulator to prevent conduction, trap air next to body Water is good conductor in water, heat will be transferred between animal and environment very quickly aquatic ectotherms must be thermoconformers

7. 16-7 2. Convection transfer of heat through bulk movement of medium e.g., currents, wind, blood flow mechanism to gain or lose heat

8. 16-8 3. Radiation transfer of heat in the form of electromagnetic radiation mechanism to gain heat when radiation absorbed by tissue mechanism to lose heat when radiation emitted by tissue If T B constant over time, 100% of absorbed radiation must eventually be re-emitted but not necessarily at the same wavelength

9. 16-9 very hot objects: emit short wavelengths cool objects: emit long wavelengths animals, earth: absorb short, emit long

10. 16-10 4. Evaporation heat loss by an organism through evaporation of water 585 cal to vaporize 1g at 22° C can be unfortunate or intentional loss

11. 16-11 5. Metabolism heat gain by metabolic burning of food “calorigenesis”

12. 16-12 Ectotherms Obtain heat by using external mechanisms conduction, convection, radiation Endotherms Obtain heat using internal mechanisms metabolism

13. 16-13 F. Ectotherms can utilize these to regulate T B Behavioral Thermoregulation Lizard in thermal gradient will move until it finds “preferred temperature” and stay there Will “defend” preferred temperature if gradient changes

14. 16-14 Things to note: 1. Maximal activity of enzymes matches preferred temperature e.g. lizards 2. Preferred temperature matches environment 3. T B can be as high as endotherms

15. 16-15 4. How is preferred temperature achieved in wild? a. internal and external T perceived by thermoreceptors in CNS and skin b. hypothalamus maintains “temperature set point” c. hypothalamus activates behaviors to thermoregulate by taking advantage of 5 mechanisms

16. 16-16 If T B < set point, work to warm up bask (absorb radiation) sit on hot rock (conduction) increase mr (metabolism)

17. 16-17 If T B < set point, work to warm up bask (absorb radiation) sit on hot rock (conduction) increase mr (metabolism)

18. 16-18 If T B > set point, work to cool off retreat to burrow (emit radiation) sit on cool substrate (conduct away) pant (evaporation)

19. 16-19 5. Advantages of Behavioral Thermoregulation Can survive on little E Ectotherm uses 1/500th the E to survive as endotherm

20. 16-20 6. Disadvantages a. No environmental E, can’t warm up enzymes need broad ranges b. If cold or warming, exposed to predators c. Difficult in aquatic environment high conductance makes it impossible to be different from T A d. Restricted to animals of small size

21. 16-21 Heat is gained across skin to warm tissue skin = surface area tissue = volume surface/volume ratio will vary with animal size surface area of an object increases as a function of length 2 volume of an object increases as a function of length 3 Therefore: as size increases, volume increases more rapidly than surface area small animal has high surface:volume ratio

22. 16-22 Alternative strategy: G. Metabolic Thermoregulation 1. Characteristics obtain heat by high mr conserve heat by good insulation

23. 16-23 2. Advantages: a. increase aerobic capacity enzymatic processes are always functioning at optimum levels adapted for immediate responses, sustained activity, endurance b. niche expansion allows maintenance of metabolic activity as animals visit habitats of varying T

24. 16-24 3. Disadvantages a. requires huge amounts of E/g BW BMR in 10 g mouse: 10 cal/g hr SMR in 10 g lizard at 37°: 1 cal/g hr especially a problem in smallest animals theoretical 5 gram minimum for endotherms b. high mr requires high ventilation rate leading to high rate of respiratory water exchange