biology 029: life on other planets… cold tolerance in ectotherms

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Biology 029: Life on other planets Cold tolerance in ectotherms Slide 2 Two strategies Freeze Avoidance Freeze Tolerance Slide 3 When its cold, water Becomes solid Becomes less dense (it expands) But it remains liquid if salt is added Slide 4 Water doesnt always freeze at 0C Small quantities of water can supercool to -20C Freezing will be induced in the presence of a nucleus Imposes structure on the water Silver iodide, certain proteins Slide 5 Application of a bacterial ice nucleating protein Slide 6 How do we know that an insect has frozen? Temperature Time Exotherm (= latent heat of crystallisation) Supercooling Point (SCP) Slide 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 Slide 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 Slide 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. Slide 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 Slide 11 Freeze Avoidance in Antarctic Fishes Trematomus bernachii (Notothenioidea) Body fluid m.p. c. -1.2 C Seawater -1.86 C Antifreeze glycoproteins Slide 12 Freeze Tolerance Survive the formation of ice inside the body Slide 13 Freeze tolerance in alpine weta Turn a freezing problem into a desiccation problem Control Ice nucleation Osmotic dehydration Slide 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 Slide 15 Adaptations to freeze tolerance and freeze avoidance Freeze tolerant Freeze avoiding SCPhighlow Ice nucleators yesno Polyolsyes Antifreeze proteins yes Slide 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 Slide 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!