Comparative Vertebrate Physiology

Temperature relations in animals

Temperature variations

Aquatic extremes -2°C - +40°C

Terrestrial extremes -65°C - +70 °C

Ectotherms in cold climates

Freezing is lethal Strategies

Freeze tolerant animals - supercooling Ca++ salts, phospholipids restrict ice formation to ECF Intracellular solutes (glycerol) restricting water

movement Freeze avoidance: depress the osmotic freezing point

Antifreeze proteins (sugars and glycerol) disrupt ice formation

Ectotherms in hot climates Critical lethal maximum

Definition (50% mortality)

Fish 35

Salamanders 29-35.6

Anurans 36-41

Alligators 38

Turtles 41

Lizards 40.1-46.9

Snakes 40.4-41.6

Terrestrial

Aquatic

Problem with hot climate Critical lethal maximum

Protein denaturing Decrease in hemoglobin O2 affinity

Ectotherm adaptations e.g.marine iguana

Bradycardia Peripheral vasoconstriction

Ectothermy Costs

Cold unless environment permits Short duration of activity Limited body size

Benefits Niche exploitation More energy for growth and reproduction Require less water

Heterotherms

Terrestrial environment (e.g. Indian python)

Heterotherms Aquatic environment: must produce metabolic heat

Fishes (rete mirabile)

Ectotherm

Heterotherm

Heterotherms Blue fin tuna

Endotherms Thermal neutral zone

Endothermy in cold climates Strategies

1. Decrease rate of heat loss Grow larger Change shape Reduce thermal conductance

(huddling, fat, migration)

Western pygmy possum

Endothermy in cold climates

• Reduce thermal conductance(countercurrent heat exchange, peripheral vasoconstriction)

Core

Appendages

37°C 32°C

25°C

5°C

15°C

10°C

22°C

12°C

7°C

artery vein

Terrestrial Aquatic

Endothermy in cold climates

Strategies 2. Increasing heat production

shivering

Endothermy in cold climates Strategies

3. Abandoning homeothermy

Torpor Hibernation

Endothermy in hot climates Strategies

Gular fluttering (birds)

Sweating (mammals)

Panting (mammals)

(evaporative cooling)

Gular

Endothermy Costs

High rate of food and water consumption High rate of respiration (water loss) Small amount of energy for growth and reproduction

Benefits Active throughout the day and night Large body size