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

Aquatic
Definition (50% mortality)
Fish
Salamanders
35
29-35.6
Anurans
Alligators
Turtles
36-41
38
41
Lizards
Terrestrial Snakes
40.1-46.9
40.4-41.6
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
37°C
32°C
25°C
22°C
artery
vein
15°C
12°C
10°C
7°C
5°C
Appendages
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