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Animal Physiology_ 2e

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					Temperature extremes.

1. Cold
   1. Dangers of ice formation
   2. How poikilotherms deal with sub-zero temperatures

2. Hot—the heat-shock response
Figure 9.22 Barnacles encased in ice during low tide along a northern seacoast
This process of crystal formation can be devastating to
cells in two ways.

1. Formation of large crystals can disrupt cell structure and membrane
integrity.

http://www.asymptote.co.uk/gallery/Videos/Eggs%201.mov
Ice front                                       2. Ice formation
                                                around cells can
 Microsterias rotata (unicellular green alga)



                                                draw out water, causing
                                                severe dehydration
                                                and shrinkage of the
                                                cell contents.
Figure 9.23 The process of extracellular freezing in a tissue
All of these species live in sub-zero environments for part of the year; but survive
by different mechanisms.




  Epiblema scudderiana (caterpillar)
  Eurosta solidaginis (fly)                      Rana sylvatica (wood frog)




                                                                       Honeybee

Box turtles, largest known freeze-
tolerant animals.                          Painted turtles
Five ways that animals deal with below zero temperatures.

1. Heat the house

2. Get out of town

3. Spend the winter as a simple stage, usually as an egg.

4. Freeze avoidance

5. Freeze tolerance.




                                         Ken Storey
Bee swarm structure as a function of
external temperature.




                              9C                       1C


           29 C                        Heinrich 1981
External      External
temperature   temperature
5C           30C




                Heinrich 1981
                    Temperature around brood in hive is
                    remarkably well regulated.




Ambient T =   3C                             25C
Five ways that animals deal with below zero temperatures.

1. Heat the house

2. Get out of town

3. Spend the winter as a simple stage, usually as an egg.

4. Freeze avoidance

5. Freeze tolerance.
                             Milkweed




Monarch



          Winter cluster in Mexico
Another way to ‘leave’ town: hide under an insulating blanket of snow.
Five ways that animals deal with below zero temperatures.

1. Heat the house

2. Get out of town

3. Spend the winter as a simple stage, usually as an egg.

4. Freeze avoidance

5. Freeze tolerance.
Five ways that animals deal with below zero temperatures.

1. Heat the house

2. Get out of town

3. Spend the winter as a simple stage, usually as an egg.

4. Freeze avoidance

5. Freeze tolerance.
Epiblema scudderiana
(moth)

                       Eurosta solidaginis
                       (fly)
                       Female Eurosta




                           Female ovipositing in
                           Solidago bud


Goldenrod (Solidago)
                           Winter
                           gall




Gall in late summer
Solidago



     Parasitic wasp that
     sticks eggs into
     gall chamber
Problem: both species live in northern areas, in galls that get very cold
during the winter (- 20 to -30°C). How do they survive?




1. Epiblema is freeze avoiding

2. Eurosta is freeze tolerant


These two strategies are quite different, but involve some of the same
  biochemical mechanisms.
Freeze avoidance




                          Gall temperature




                   Supercooling point of
                   larvae
Super cooling of aqueous fluids
Trace of water temperature in a straw that was gradually cooled.
Ice didn’t form spontaneously until about -15°C.




                                                         Heat of
                                                         crystallization
This graph shows a frequency histogram of ice nucleation temperatures
for pure water in a small straw cooled at about 0.3°C per minute.




                                                 Supercooling
                                                 is easiest in
                                                 small volumes
                                                 of water—which
                                                 is what insects
                                                 are: insects
                                                 naturally supercool
                                                 to about -10°C
 How to depress the supercooling point as much as possible?


1. Increase the solute concentration, usually by using small polyhydric
   alcohols (e.g., glycerol, sorbitol)

2. Use proteins that inhibit the formation of ice crystals.

3. Avoid contact with ice that can seed further ice formation.


    Polyhydric alcohols
         carbon
hydrogen

                     oxygen




   Ethanol (not                   Glycerol (common               Ethylene glycol
   used as a                      cryoprotectant)                (the antifreeze
   cryoprotectant)                                               in your car’s
                                                                 radiator).
3 M glycerol!

                Epiblema scudderiana


                In mid-winter, glycerol
                can make up 20 – 25% of
                the insect’s total body mass.




                The glycerol is manufactured
                from large stores of glycogen.
 A January 2010 article in Journal of Experimental Biology



Deep supercooling, vitrification and limited survival to
–100°C in the Alaskan beetle Cucujus clavipes puniceus
(Coleoptera: Cucujidae) larvae

T. Sformo1,*, K. Walters2, K. Jeannet1, B. Wowk3, G. M. Fahy3,
B. M. Barnes1 and J. G. Duman2
Another solution: make antifreeze proteins. These proteins bind
to small ice crystals and prevent them from growing.
Freezing points of aqueous solutions containing major sugars, salts and glycoproteins used
as antifreeze agents.


                                                      These glyco-
                                                      proteins from
                                                      Antarctic fish.
                                          Liou et al. 2000




Structure of antifreeze protein from Tenebrio molitor
(mealworm beetle)
AFP




Ice



The AFP is structured so
that it fits exactly into the
2-D structure of the ice lattice
(probably by hydrophobic
interactions).




           Liou et al. 2000

				
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