Marine Mammal
Thermoregulation
Protein Nitrogen
Urea
Heat
Salts
Na, Cl, K
Fuel + O2
Energy & Work
Salts
Na, Cl, K
CO2 + H2O
Water
Water
Protein Nitrogen
Urea
Heat
Salts
Na, Cl, K
Fuel + O2
Energy & Work
Salts
Na, Cl, K
CO2 + H2O
Water
Water
Thermoregulation
Heat capacity or thermal mass?
Measure of the ability of a substance to store heat kJ g-1
Extrinsic property = varies with characteristics of object
Size, mass, volume etc
Definitions
• Poikilotherm
– temperature conformer: Tb ≈ Ta
• Homeotherm
– temperature regulator: Tb ≈ constant
• Endotherm
– Endogenous heat production to maintain Tb
• Ectotherm
– External source of heat production to maintain Tb
• Thermoregulation
– Process of regulating body temperature
Definitions
• Poikilotherm
– temperature conformer: Tb ≈ Ta
• Homeotherm
– temperature regulator: Tb ≈ constant
• Endotherm
– Endogenous heat production to maintain Tb
• Ectotherm
– body temperature derived from environment
• Thermoregulation
– Process of regulating body temperature
Thermoregulation Challenges
• Marine environment colder than Tb
• Water conducts heat ~25x faster than air
• Amphibious marine mammals (pinnipeds)
thermoregulate in air & water
Maintaining Thermal Balance
Heat loss = Heat production
Heat loss
• Convection = heat transfer to a fluid (movement of
air or water)
• Conduction = heat transfer to a solid
• Radiation = transfer of radiant energy
• Evaporation = heat absorbed from phase change
liquid to water vapor (respiratory water loss)
Maintaining Thermal Balance
Heat loss = Heat production
convection
radiation
evaporation
conduction
Heat transfer associated with:
• Surface area
– varies with Mass2/3
• Temperature differential
- b/n environment (Ta) & body (Tb)
Heat loss = Conductance * Surface area * (Tb - Ta)
Conductance of Common Materials
Material
Silver
Aluminum
Iron
Otariid blubber
Human fat
Whale blubber
Phocid blubber
Dolphin blubber
Wood (white pine)
Animal fur
Air
k (W/m C)
428
235
80
0.17-0.39
0.21
0.18-0.21
0.18-0.20
0.10-0.20
0.11
0.038
0.024
Conductors
Insulators
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
– Tb
– Typical Mammalian Tb = 36-38 oC
– Cetaceans Tb = 35.5 oC
Lowering Body Temperature (Tb)
• Generally occurs while diving
• May lower body temp to reduce O2
consumption
– Hypometabolism
• Promotes longer dive times
cADL =
O2 stores
O2 consumption
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
–
Tb
• Increase body size
–
surface area to volume ratio
Surface Area : Volume Ratio
Surface area = 6 (3x )2
Volume = (3x )3
Marine Mammals Are Large
Clauset A (2013) How Large Should Whales Be?. PLoS ONE 8(1): e53967. doi:10.1371/journal.pone.0053967
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053967
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
–
Tb = 36-38 oC
• Increase body size
–
surface area to volume ratio
• Increase metabolism
–
heat production
Metabolic Rates Seem To Be
Elevated In Some Species
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
Mass 0.75
(Kleiber)
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Metabolic Rates Seem To Be
Elevated In Some Species
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Metabolic Rates Seem To Be
Elevated In Some Species
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Metabolic Rates Seem To Be
Elevated In Some Species
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Thermal Neutral Zone (TNZ)
• Range of environmental temperatures an
animal can maintain Tb without increasing
metabolism
Thermal Neutral Zone (TNZ)
Thermal Neutral Zone (TNZ)
Thermal Neutral Zone (TNZ)
Thermal Neutral Zone (TNZ)
Adult sea lion thermal capabilities
Resting Metabolic Rate (mLO2·min-1·kg-1)
Adult sea lions are thermally neutral at routine water temperatures.
14
Adult1
Adult2
Adult3
Adult4
Adult5
12
10
8
6
4
TLC = 6.4 ± 2.2 °C
2
0
5
10
15
20
Water Temperature (°C)
(Liwanag et al., 2009, JEB)
Thermal Neutral Zone (TNZ)
Sea otter
Sea lion
Dolphin
(Morrison et al., 1974; Costa & Kooyman, 1984;
et al.,&1998;
Mostman-Liwanag
etet
al.,al.,
in 1998)
prep)
(Morrison et al.,Williams
1974; Costa
Kooyman,
1984; Williams
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
–
Tb = 36-38 oC
• Increase body size
–
surface area to volume ratio
• Increase metabolism
–
heat production
• Increase insulation
–
conductance
Two Ways to Increase Insulation
•
blubber layer
•
density or length of hair
– Sea otters: 125,000 hairs per cm2
Type of insulation depends on the
species & habitat
Insulation
Fur:
• Traps air
among the hairs
• Air provides the
insulation!
Insulation
Blubber:
• continuous sheet
of adipose tissue
• reinforced by
collagen & elastic
fibers
Insulation:
Fur seal vs. Sea lion vs. Phocid
Cross Section of Seal Carcass
Advantages
Blubber
Disadvantages
• Live tissue at low
temps
• Difficult to grow or
divide at low temps
• Must haul out to molt
& heal
• Can withstand
fouling
• Does not
compress with
depth
• Able to dump heat
• Energy store
Fur
Temperature
differential
between skin &
tissue
Temperature Differential of the Skin
in Water vs. in Air
Coping With the Cold Ocean
Amphibious Lifestyle
Advantages
Blubber
• Live tissue at low
temps
• Difficult to grow or
divide at low temps
• Must haul out to molt
& heal
• Can withstand
fouling
• Does not
compress with
depth
• Able to dump heat
• Energy store
Advantages
• Lighter
• Better insulation
for given amount
• Skin is
maintained at or
near body temp
– Ability to repair
skin, molt, etc.
Disadvantages
Fur
Disadvantages
• Requires air layer
• Needs to be kept
clean
• Insulation declines
with depth
Diving with fur
• Loss of air = loss of insulation
• Requires extensive time
grooming at surface
Thermal Windows
Poorly insulated areas through which heat dissipates
Thermal Windows
Norris et al
2010 JEB
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
–
Tb = 36-38 oC
• Increase body size
–
surface area to volume ratio
• Increase metabolism
–
heat production
• Increase insulation
–
conductance
• Vascular control
– counter-current heat exchange
How do you keep heat loss low to periphery
yet still keep blood flowing to it?
Counter Current
Heat Exchanger
Countercurrent arrangements
Peripheral Blood Vessels
Gray Whale Tongue
(a cool meal)
Tongue
Arteries transport blood to tongue
Veins return blood to body
Heat flow
Problem:
Internal
Testes
Cross Section
Through
Dolphin At
The Level Of
The Testes
Why don’t the dolphin testes “fry”?
Cool temperatures important
for spermatogenesis
Why don’t the dolphin testes “fry”?
Cool temperatures important
for spermatogenesis
Cool blood from fins
& fluke
Why don’t the dolphin testes “fry”?
Cool temperatures important
for spermatogenesis
Cool blood from fins
& fluke
Cools core blood before
reaching testes
Temperature Regulation for Testes
Marine Mammal Strategies
for Thermoregulation
• Lower temperature differential
–
Tb = 36-38 oC
• Increase body size
–
surface area to volume ratio
• Increase metabolism
–
heat production
• Increase insulation
–
conductance
• Vascular control
– counter-current heat exchange
• Behavioral thermoregulation
Behavioral Thermoregulation
Haul out when warm in polar regions
Behavioral Thermoregulation
Haul out when warm in polar regions
Healing
Crabeater Seal
(Lobodon carcinophaga)
Behavioral Thermoregulation
Clump together when cool or to save heat
Behavioral Thermoregulation
Clump together when cool or to save heat
Catastrophic Molt
Behavioral Thermoregulation
Lie in water when warm
Behavioral Thermoregulation
Sand Flipping
How do these animals acclimate to
seasonal changes?
Seasonal Changes
• Dolphins change their blubber
• Quantity – seasonal changes in thickness
Seasonal change in thickness
Seasonal change in thickness
Seasonal Changes
• Dolphins change their blubber
• Quantity – seasonal changes in thickness
• Quality – seasonal changes in composition:
straight chain
(saturated) fats
bent chain
(unsaturated) fats
• Better insulation
• Poorer insulation
What about pups?
• Lanugo: “birth coat”
– Dense coat of very fine hair
– Works in air (not waterproof)
Born with lanugo & brown fat
What about pups?
• Brown fat
• Specialized adipose tissue
• Non-shivering thermogenesis
California Sea Otter –
smallest marine mammal
Resting metabolic rate (W)
10000
Odontoceti
Sirenia
Phocidae
Otariidae
E. lutris
1000
100
2X
ed
dict
e
r
P
ted
c
i
d
Pre
10
10
100
Mass (kg)
1000
Metabolic Rate In Relation To
Water Temperature
Temperature (°C)
Sea otter allows body temperature to
change
Uses feeding to keep warm