Thermoregulation Flashcards
What is one of the main challenges of ocean living?
Water is more conductive than air
Why does thermoregulation have important implications for energetics?
Marine mammals must have adaptations that allow them to thermoregulate while using as little energy as possible. The more energy that is spent on thermoregulation (metabolism) the less energy the organism has for reproduction, and growth (energy is finite).
Homeothermy
Maintenance of a constant body temperature warmer than that of the environment (warm-blooded)
Endothermy
Use of and elevated metabolism to maintain homeothermy
Ectothermy
Reliance on an external heat source (ex: the sun) to maintain an elevated body temperature
Poikilothermy
Failure to regulate body temperature, conformance to ambient temperature (cold-blooded)
Conductance
Transfer of heat between two substances in direct contact with one another
Convection
Transfer of heat through a medium (ex: air)
What is the most important form of heat loss for marine mammals?
Conductive heat loss
Describe the relationship between conduction and insulation
Conductance is the inverse of insulation
A decrease in conduction will result in a decrease in heat loss and an increase in insulation
How can marine mammals reduce heat loss?
- Large body sizes: smaller SA to volume ratio
- Reduction in surface area to volume ratio: less SA to loose heat
- Decrease thermal conductance (ex: blubber, fur)
Do larger organisms have a high or low SA to volume ration?
Low
What are ecogeographic rules?
Describe the variability in morphological traits of animals over geographical gradients
- Bergmann’s rule
- Allen’s rule
Describe Bergmann’s rule
Populations and species show larger body sizes closer to the poles (colder environments), Away from the poles (warmer environments) populations and species exhibit smaller body sizes.
Explain the reasoning behind Bergmann’s rule
- Larger animals are better adapted to colder environments
- Lower SA to volume ratios (reduced heat loss)
- Ex” Long-finned vs Short-finned pilot whales
How do marine mammals that are smaller in size (ex: sea otter, and fur seals) reduce their thermal conductance?
- Fur
- Dense fur traps air
- Sebaceous glands: secrete wax that water proofs fur
- Squalene (sea otters): hydrophobic lipid barrier effective against water
What are some disadvantages of fur?
- Not as smooth as blubber
- Air gets compressed in diving marine mammals (looses its effectiveness as an insulator)
Only dense fur can retain insulate properties when submerged in water
Blubber
- Lipid rich hypodermis
- Found directly under the skin
- Highly modified form of adipose tissue
What are the functions of blubber?
- Insulator
- Adjusts buoyancy
- Defines body shape and streamlines
- Serves as an energy depot
- Acts as a biological spring
What are some factors that affect the insulative properties of blubber?
- Thickness
- Lipid content (more lipids = better insulation)
- Blood flow
Describe the relationship between temperature and blubber lipid content
The colder the temperature, the higher the organisms bubbler lipid content
What are important factors related to the lipid content of blubber?
- Body size
- Thermal habitat
Cooler water species = high lipid content, warmer water species = lower lipid content
Describe the differences in the stratification of blubber for organisms that live in warm and cold environments
Organisms in colder environments exhibit more stratification that organisms in warmer environments
- Outer layer: structural and thermoregulatory purposes
- Inner layer: metabolically active
What marine mammals use fur as an insulator?
- Sea otters
- Fur seals
- Polar bears
What marine mammals use blubber as an insulator?
- Phocid seals
- Cetaceans
- Sirenians
What is a common misconception about marine mammals in regards to thermoregulation?
“Marine mammals are wrapped like a thermos bottle”
Although marine mammals utilize blubber to stay warm, they must also be able to cool down when needed
Regional heterothermy
The ability to control body temperature in at least one region of the body in isolation from other regions
Letting different parts of your body be different temperatures
What adaptations do marine mammals have that allow them to dissipate heat?
- Thermal windows
- Differential blood flow (vasodilation)
- Counter-current heat exchange
Thermal windows
Thinly insulated flippers and fins can give off heat if needed
Counter-current heat exchange
Maximize the flow of heat from warm arteries (traveling from the body’s core) to relatively cool veins (traveling from the extremities). As the blood flows in opposite directions, the amount of heat that is transferred is increased. This helps maintain the organisms core body temperature and reduce heat loss to the environment.
How do marine mammals prevent body heat from being continuously lost through thermal windows?
- Two venous return systems or pathways
- One lies close to the surface of the skin, the other forms a countercurrent heat exchanger with the arteries that connect to the fins, flippers, and flukes
- To conserve heat, the organism will use the counter-current exchange pathway
- To dissipate heat, the organism will use the pathway of “superficial veins” so that body heat can be transferred to the fluid environment
Describe reproductive thermoregulation
- Phocids, Sirenians, and Cetaceans have cryptic testes
- Mammalian sperm production is optimized several degrees below core temperatures
- The scrotum act as a thermal window (allows heat to be exchanged between the testes and the external environment)
The reproductive thermoregulation of marine mammals is an example of…
Convergent evolution
Organisms that are not closely related develop similar traits to one another based on similar environmental pressures
Describe Allen’s rule
The limbs, ears, and other appendages of endothermic animals living in cold climates tend to be shorter than animals living in warm climates
Why
Do marine mammals follow Allen’s rule?
No
Long-finned Pilot Whales (colder) have longer appendages than Short-finned Pilot Whales (warmer)
Why is Allen’s rule not upheld with Pilot Whales?
Large-finned Pilot Whales have highly insulated bodies that require mechanisms for rapidly dissipating heat (thermal windows) after exercise
What is the thermal neutral zone?
Range of temperatures where an organism can maintain its core body temperature without an increase in their metabolic rate
What is the thermal neutral zone bounded by?
An upper critical temperature and lower critical temperature
Describe the metabolic rate within the thermal neutral zone
It is the standard metabolic rate for that organism (no increases)
