L7 Temp 2 PDF - Comparative Animal Physiology

Temperature II - Coping with extremes Comparative Animal Physiology 1 Learning Outcomes By the end of this lecture you should be able to: Briefly detail what issues extreme temperatures pose List, describe and give examples of the mechanisms by which differe...

Temperature II - Coping with extremes Comparative Animal Physiology 1 Learning Outcomes By the end of this lecture you should be able to: Briefly detail what issues extreme temperatures pose List, describe and give examples of the mechanisms by which different animals cope with extreme temperatures Explain the interrelations between the temperature, water, and nutritional budgets of an organism 2 Thermal extremes  How do animals attempt to maintain survival when exposed to extreme temperatures? optimal Fitness death survival reproduction survival death 0 5 10 15 20 25 30 35 40 45 50 Temperature ºC 3 Cold – the problem  Biochemical reactions have an optimal range and occur more slowly with decreasing temperatures  Disruption of cell membrane function - loss of selective permeability and transport processes  Ice crystal formation – Points and edges can pierce membranes – Crystal growth removes surrounding water 4  Cold – coping strategies Metabolic rate  Prevent heat loss  Increase heat production/gain  Riding it out 5 Prevent heat loss - insulation  Insulation: a layer of material that reduces thermal exchange  Ubiquitous in endotherms – cost reducing  Rarer in ectotherms Feathers Fur Setae Gypsy moth caterpillar Flame robin Marsupial mole Blubber Australian fur seal Little penguin Spinner dolphin 6 Caterpillar setae: insulation for an ectotherm. Casey & Hegel. Science. 1981 Dec 4;214(4525):1131-3  Prevent heat loss – insulation acclimation  Seasonal change in insulation levels Animal Physiology 3rd Hill et al 2012. Figure 10.40b 7 Prevent heat loss - behaviour  Reduce whole body exposure to cold Orcas and Weddell seal  Burrow  Water  Migrate  Posture  Reduce surface area/extremities  Reduce air/skin interface  Increase ‘thickness’ of insulation Field mouse Junco - Piloerection Honeybees  Huddling/grouping Emperor penguins  Prevent heat loss – regional heterothermy  Allowing some tissues to cool can be advantageous  Appendages are potential sites of major convective heat loss  Restrict blood flow to regions/tissues  Reduces heat loss/energy expenditure  Metabolically ‘inactive’ tissues  Common in endotherms  Vasoconstriction  Occurs in ectotherms  Vasoconstriction  Slowing heart rate Animal Physiology 3rd Hill et al 2012. Figure 10.32b Seebacher & Franklin (2007). J. Comp. Physiol. B 177,841 -848 9  Prevent heat loss – countercurrent exchange  Countercurrent exchange preserves core temperature  AND tissue O2 supply Stops penguin’s feet Red swimming muscles in freezing tuna and lamnid sharks Animal Physiology 3rd Hill et al 2012. Fig 10.32 Principles of Animal Physiology Moyles et al 2014 Fig 13.23 10  Increase heat production/gain  Behaviour  Voluntary physical activity Honeybee beating wings  Seeking/orienting to heat sources  Increase metabolic rate - endotherms Japanese macaques  Cold-induced thyroid stimulating in hot springs hormone (TSH) release  Increased heat production  Increased nutrient requirement Life: the science of biology 8th, Purves et al Hill et al 2007 Fig 40.9 11 Increased heat production - thermogenesis  Thermogenic mechanisms - Specifically increase heat production  Shivering  Common to all mammals and birds (some insects)  Unsynchronised contraction & relaxation of skeletal muscle units  Random (not synchronized locomotor) antagonistic movement  Produces more heat as no energy lost to external work  Non- shivering thermogenesis  Placental mammals  Cold-acclimated, hibernators & newborn  Brown adipose tissue (BAT)  Increased rate of lipid oxidation  Lipid catabolic energy released immediately as heat BAT distribution in a newborn rabbit Adapted from Animal Physiology 3rd Hill et al 2012. Fig 10.31 12  Riding it out – controlled hypothermia  Controlled hypothermia  Hibernation: reduced MR and TB ≈ TA over prolonged winter/cold periods  Daily torpor: reduced MR and TB < 32 ⁰C for ≤ 24hrs  Temporal heterothermy  Escape demands of homeothermy  Energy saving related to TA  MR – metabolic rate  TB – body temperature  TA – ambient temp Daily torpor in the dunnart (Smithopsis macroura) Geiser, F. (2004). Metabolic rate & body temp reduction during hibernation &daily torpor. Ann Rev Phys 66, 239 13 Riding it out – controlled hypothermia 14 Riding it out – freeze tolerance/avoidance Freeze-avoidance - mechanisms to prevent ice crystal formation and growth  Antifreeze compounds – lower freezing point of body fluids  Solutes with chemical properties that disrupt ice crystal growth (glycerol & glucose)  Supercooling – prevent freezing of body fluids  Remove nucleators from body fluid – prevents ice crystals forming Freeze-tolerance – allow tissues to freeze  Nucleator compounds  Produced outside of cells, limit location of ice crystal growth to extracellular  Antifreeze compounds  Particularly glycerol & glucose 15 Heat – the problem  Proteins denature faster at high temperatures  Accumulation of denatured proteins can kill the cell  Heat shock proteins (Hsp’s) – molecular chaperones that catalyze protein folding after translation and help refold denatured proteins  Heat shock response – increase in the levels of Hsp’s in response to extreme temperatures 16 Hot – coping strategies  Increase heat loss/avoid heating  Decrease heat production/gain  Riding it out 17  Increase heat loss/avoid heating - behaviour  Reduce exposure to heat Cape Ground Squirrel  Seek Shade  Seek Water  Migrate  Nocturnal  Posture Zebra-tailed lizard  Orient away from solar gain  Minimise conductive gain  Increase air/skin interface  Minimise activity Bennett et al. 1984. The parasol tail and thermoregulatory behavior of Briscoe et al. 2014.. Biology Letters 10:20140235. the Cape Ground Squirrel Xerus inauius. Physiological Zoology 51:57-62. 18 Avoid heating - colour Winter Summer Addax (Addax nasomaculatus) 19  Increase heat loss - vasodilation  Redistribute blood flow to skin and/or conductive appendages  Blood cooled at surface reduces core temperature  Vasodilation – cutaneous circulation Fennec fox African elephant Black-tailed jackrabbit http://www.bbc.co.uk/nature/16657090 20  Increase heat loss – selective brain cooling  Countercurrent exchange to preserve brain temperature  Some mammals and birds e.g. camel, dog, sheep, gazelle Animal Physiology 3rd Hill et al 2012. Fig 10.37 21 Increase heat loss - evaporation  Evaporation – last line strategy for reducing heat load  Water loss can lead to dehydration Panting  Increased respiratory rate  Evaporative cooling from respiratory surfaces  Advantage: don’t lose salts & creates air flow  Disadvantage: requires external work Gular flutter  Rapidly vibrate their gular (floor of buccal cavity) with mouth open  Birds Collard pratincole 22  Increase heat loss - evaporation Sweating  Few animals have effective sweat glands  Evaporative cooling from saline solution on skin  Under autonomic control  Humans, horses, camels and some kangaroos Saliva/excretion  Produce/spread fluids  Saliva spreading: e.g. rats & kangaroos  Excretion: e.g. black vultures excrete on their unfeathered legs  Increased mucous production: e.g. Rana catesbiana Lillywhite, Thermal modulation of cutaneous mucus discharge as a determinant of evaporative water loss in the frog, Rana catesbeiana Journal of Comp Physiol 1971, Volume 73,1, pp 84-104 23 Riding it out – cycling body temperature  Dehydrated camels allow body temperature to vary by more than 6°C  Day: - store heat in the body by allowing TB to rise to up to 40⁰C  Night: - lose heat to cool air and night sky (TB =34-35⁰C)  Can save > 3L water per day! Knut Schmidt-Neilsen Photo: wikimedia commons 24 Riding it out - estivation  Australian water-holding frog (Cyclorana platycephala)  Estivates during periods of hot, dry weather  Creates a cocoon out of mucus secreted from its skin  Buries itself underground: cooler, stable environment reduces TB and metabolism 25 Hypothalamus – mammalian thermostat  Temperature sensitive neurons/nerve endings exist in brain, spinal cord, skin, and internal core  Sensors in hypothalamus particularly sensitive in mammals  Three subsets of neurons in hypothalamus with different sensitivities and responses  But not consistent outside mammals  Fish, amphibians and reptiles – triggers behavioral thermoregulation, and some physiological responses (eg panting)  Birds – does nothing 26 Learning Outcomes By the end of this lecture you should be able to: Briefly detail what issues extreme temperatures pose List, describe and give examples of the mechanisms by which different animals cope with extreme temperatures Explain the interrelations between the temperature, water, and nutritional budgets of an organism 27 QUESTION: (i) Explain 3 mechanisms by which animals exchange heat with their environment (each explanation must include a description of the mechanism of thermal movement/heat exchange and a physiological example from an animal). (6 marks) (ii) Explain, with two examples, how a lizard might change its behaviour to cool down on a hot day (make sure you explain the mechanism by which the behaviour works) (4 marks). 28