1. Biology 029: Life on other planets… Cold tolerance in ectotherms

2. Two strategies  Freeze Avoidance  Freeze Tolerance

3. When it’s cold, water…  Becomes solid  Becomes less dense (it expands)  But it remains liquid if salt is added

4. Water doesn’t always freeze at 0°C  Small quantities of water can supercool to -20°C  Freezing will be induced in the presence of a nucleus Imposes ‘structure’ on the water Silver iodide, certain proteins

5. Application of a bacterial ice nucleating protein

6. How do we know that an insect has frozen? Temperature Time Exotherm (= latent heat of crystallisation) Supercooling Point (SCP)

7. Freeze Avoidance  Keep body fluids liquid at temperatures below their melting point  Theoretical lower limit c. -50 °C  Probability of freezing is proportional to Temperature Time Volume

8. Freeze Avoidance Adaptations  Colligative Antifreezes Sugars and Polyols eg: Glycerol, Trehalose More stuff = lower melting and freezing points 1 Mole of solutes = -1.86 °C

9. Freeze Avoidance Adaptations  Non-colligative antifreezes Antifreeze proteins and glycoproteins aka Thermal Hysteresis proteins Act to prevent the growth of ice crystals in solution Depress the freezing point much more than would be predicted by their concentration.

10. Antarctic Springtail 0 0.5 1 1.5 Thermal Hysteresis (°C) 30 Nov 9 Dec 24 Dec 31 Dec 10 5 55 Antifreeze proteins 30 20 10 0 -30 0-10 -20 Frequency 21 Oct 1999 Median: -35.4 °C SCP (°C) mean SCP (°C) ln [glycerol] Gomphiocephalus hodgsoni Ross Island, Antarctica

11. Freeze Avoidance in Antarctic Fishes  Trematomus bernachii  (Notothenioidea)  Body fluid m.p. c. -1.2 °C  Seawater -1.86 °C  Antifreeze glycoproteins

12. Freeze Tolerance  Survive the formation of ice inside the body

13. Freeze tolerance in alpine weta  Turn a freezing problem into a desiccation problem Control Ice nucleation Osmotic dehydration

14. Freeze tolerance adaptations in insects  Ice Nucleation Control it!  Polyols Protect membranes and proteins Act as stuffing for osmotically dehydrated cells  Antifreeze proteins Inhibit recrystallisation

15. Adaptations to freeze tolerance and freeze avoidance Freeze tolerant Freeze avoiding SCPhighlow Ice nucleators yesno Polyolsyes Antifreeze proteins yes

16. Adaptations to freeze tolerance and freeze avoidance Freeze tolerantFreeze avoiding SCPSlow freezingDie when freeze Ice nucleatorsInitiate freezing easily Prevent initiation of freezing PolyolsProtect membranes and proteins; act as ‘stuffing’ Protect membranes and proteins; depress SCP Antifreeze proteins Prevent recrystallisation Reduce chance of freezing

17. Vertebrate freeze tolerance! Also some lizards, salamanders & hatchling turtles… Wood Frog (Rana sylvatica) Nearly 70% of body water converted into ice (extracellular) Can survive being frozen for at least 4 weeks!