Freeze Tolerance Flashcards
(25 cards)
What is freeze tolerance?
The ability for some insects and vertebrate species to tolerate a certain percentage of their extracellular space to be frozen.
When is freeze tolerance favoured?
In unpredictable, cold environments
What are the mechnisms involved in freeze tolerance?
Nucleating proteins
Cryoprotectants
Ice-binding proteins
Membrane transporters
What do ice nucleating proteins do?
They induce and regulate extracellular freezing to stop ice from growing inside the cell
What are ice-binding proteins?
They bind to the ice crystals to stop them from growing too much
What are cryoprotectants?
Molecules that are synthesised in the liver and transported to the cells to retain water inside the cells and minimise the loss of water to the ice
What are membrane transporters?
They efficiently move water and cryoprotectants in and out of the cell
What is the process of freeze tolerance in wood frogs?
- Body temp reduces below 0’C and initiates freezing on the surface of their bodies
- They increase their metabolism so that they can produce more cryoprotectants (glucose)
- Their cardiovascular function remains intact until ice starts to penetrate the frog
- Their HR declines until circulation is lost and there is no muscular activity
What happens when temperatures start to increase in wood frogs?
- Their heart starts to beat again
- Breathing returns, followed by eye twitching and then leg movement
- Can take days to return to normal
What are the advantages of freeze tolerance in wood frogs?
- They can breed earlier than other species as they can detect changes in temperature (more food, less predators)
- They can breed in safer places
Where are cryoprotectants mostly found in wood frogs?
The eyes and the brain as they must protect these
What are the advantages to freeze tolerance?
Can survive if freezing occurs suddenly
Can tolerate temperatures below their SCP
Can survive in exposed environments
What are the disadvantages to freeze tolerance?
Ice can cause cellular and tissue damage
Repair is expensive
May take them longer to recover from freezing
Producing freeze tolerance mechanisms is expensive
Limited mobility during the cold
What is the difference between the Alaskan and Ohioan wood frogs?
Alaskan: Can tolerate more extreme temps, longer freezing time (8 months), can cool at faster rates (2’C per hours)
Ohioan: less extreme temps (-6’C), shorter freezing period, cool at a slower rate
What does freeze tolerance look like in brown tree frogs?
Only SH vertebrate known to be freeze tolerant.
Can survive freezing at -1’C for 6-12 hrs.
Produces glycerol during cooling and glucose during thawing.
What is freeze tolerance in insects?
Can survive 80% of their EC fluids being frozen.
Some can survive IC freezing.
Their lower lethal temp ranges from -11 to -196’C.
Varies between seasons and life stages.
What type of freezing do frogs have?
Active freezing by increasing MR once it reaches a certain temp where ice starts to form on their skin
What type of freezing do insects have?
Passive freezing that is a physical and chemical response
When does ice formation occur in insects?
Most insects can supercool and then ice formation accounts beyond their SCP
When do insects thaw?
When the temperature is above melting point
What mechanisms do insects use for freeze tolerance?
Cryoprotectants
Ice nucleating agents
Antifreeze proteins
Recrystallisation-inhibiting proteins
What do recrystallisation-inhibiting proteins do?
They stabilise ice crystals and stop them from growing and spreading
What type of cryoprotectants do insects produce?
Glycerol
Proline or trehalose to protect the membrane by replacing water in their structures
What do ice nucleating agents do?
They are not always proteins and are found in different parts of the of the body where they initiate freezing
