1. 29-1 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Chapter 29: Animals responding to environmental stress

2. 29-2 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Phenotypic plasticity Some organisms can modify phenotype to accommodate changes in environment –phenotypic plasticity Such changes are categorised as –acclimatisation: accommodating several changes in environment –acclimation: accommodating one change in environment –hardening: acclimation in plants

3. 29-3 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Stresses of the arid zone Arid zone of Australia characterised by –high daytime temperatures –extended periods of low rainfall –intermittent floods Most animals avoid high temperatures rather than tolerate them –burrow –active during cooler periods (dawn, dusk, night) Most animals do not require drinking water

4. 29-4 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Termites in arid Australia Termites build substantial nests above ground Maintain constant temperature –thick wood-pulp walls insulate nest –north-south orientation of ‘magnetic’ termite mounds reduces exposure to midday sun –internal passages allow air to circulate –high humidity is maintained by transporting water from water table

5. 29-5 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Stresses of low temperatures Mountain and polar regions are characterised by –low temperatures –increased solar radiation Animals of cold regions are more tolerant of low temperatures than other animals Ice formation damages cells by concentrating cytoplasm and dehydrating proteins

6. 29-6 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Do animals freeze? Animals in areas that experience low temperatures may –avoid freezing by supercooling –tolerate freezing During supercooling, the temperature may drop below 0°C, but ice does not form in the animal’s tissues –evacuate body of material that might seed ice formation –produce antifreeze that prevents ice formation and/or lowers freezing point

7. 29-7 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Insects at low temperatures Insect species that live at high altitude tend to be small and wingless –able to make use of sheltered microhabitats Many species exhibit thermal melanism –dark coloration absorbs heat Basking in sun increases body temperature –some insects bask in light-coloured flowers that reflect heat

8. 29-8 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Temperature coefficient Q 10 Biochemical processes take place within a range of temperatures –rate of activity increases with temperature Temperature coefficient, Q 10, models the rate of reaction for a 10°C rise in temperature Quantifies effect of temperature on biochemical processes

9. 29-9 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 29.4: Relationship between process and temperature

10. 29-10 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Temperature regulation Endothermic animals (birds, mammals) maintain a constant body temperature by deriving heat from internal or metabolic processes Ectothermic animals cannot regulate body temperature through those processes, but can reduce fluctuations in body temperature by adjusting behaviour

11. 29-11 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Thermal acclimation Although metabolic processes in ectothermic animals tend to increase with temperature, thermal acclimation means that metabolic rate may change between seasons –cold-water fish may have higher metabolic rate in winter than they have in summer Seasonal metabolic compensation –different sets of summer and winter enzymes with different optimal temperatures –animals may be more active in winter than summer, despite lower temperature

12. 29-12 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Metabolic depression Facing extreme conditions, many animals undergo a reduction in metabolic rate (metabolic depression) Some organisms can reduce metabolic rate to less than 1 per cent of normal resting metabolic rate Animals survive by dehydrating as larvae or adults, aestivating or becoming inactive

13. 29-13 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Hypothermia and torpor Endothermic animals undergo –prolonged hibernation during winter –prolonged aestivation in dry conditions –shorter periods of torpor Body temperature is reset to a lower level –hypothermia –metabolic processes drop as a result –decreased responsiveness to stimuli

14. 29-14 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Risks of torpor Freezing –use of cryoprotectants such as glucose to prevent freezing Lack of oxygen –many animals can tolerate anoxia Exhaustion of energy supply –breakdown of lipids using anaerobic pathways to avoid using O 2 Desiccation

15. 29-15 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Torpor Many small mammals and some birds reduce metabolic rate and enter torpor in response to low temperatures Body temperature is regulated during torpor –if it drops too far, animal becomes active for a period before re-entering torpor Blood flow to skin and extremities is reduced during torpor

16. 29-16 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 29.8: Rate of O 2 consumption in dunnart

17. 29-17 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Environmental oxygen stress Hypoxia is decrease in partial pressure of O 2 from normal levels Occurs when rate of O 2 consumption exceeds replenishment –caves, burrows –swamps, water-logged soil –tide pools Occurs at high altitudes where P O 2 is low

18. 29-18 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Adaptations to low oxygen Low environmental P O 2 reduces the gradient essential for diffusion of O 2 across membranes Physiological and behavioural characteristics compensate for low P O 2 –tolerance to anoxia –haemoglobin –high erythrocyte counts –low rates of O 2 consumption –burrow ventilation

19. 29-19 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Responses to high altitude Lower partial pressure of oxygen in high altitudes produces altitude hypoxia Hyperventilation is a response to low P O 2 –increases O 2 content Hyperventilation also eliminates CO 2 from body, causing high blood pH Erythrocyte count may increase as a result of acclimation –higher levels of haemoglobin

20. 29-20 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Oxygen stress When faced with a thermal gradient, animals have a preferred temperature –behavioural thermoregulation When exposed to hypoxia, animals choose a lower temperature –hypoxia depresses thermogenesis (metabolic heat production) in endotherms –set point of body temperature lowered (cont.)

21. 29-21 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 29.16: Distribution of Daphnia carinata

22. 29-22 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Oxygen stress (cont.) Reduced temperature decreases metabolic rate (Q 10 effect) Decreased requirement for O 2 Reduction in temperature increases O 2 affinity of haemoglobin Hyperventilation and increased cardiac output are avoided (cont.)

23. 29-23 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Oxygen stress (cont.) Depression of thermogenesis in response to hypoxia is more common in small animals than in large animals –large animals have a lower mass-specific metabolic rate, so use proportionately less O 2 to maintain body temperature –smaller surface area in relation to body volume means that large animals do not absorb or lose heat as rapidly

24. 29-24 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Global warming Increase in temperature as a result of global warming may stress less thermally-tolerant organisms –increased sea temperatures have a negative impact on penguin species –migrations of some bird species start earlier in the year –breeding is brought forward or delayed –species’ ranges are extended or retracted

25. 29-25 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 29.18: Mean values of spring phenological shifts