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Biology 029: Life on other planets…

Biology 029: Life on other planets…. Cold tolerance in ectotherms. Two strategies. Freeze Avoidance Freeze Tolerance. When it’s cold, water…. Becomes solid Becomes less dense (it expands) But it remains liquid if salt is added. Water doesn’t always freeze at 0 °C.

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Biology 029: Life on other planets…

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  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? Exotherm (= latent heat of crystallisation) Temperature Supercooling Point (SCP) Time

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

  16. Adaptations to freeze tolerance and freeze avoidance

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

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