Chapter 3

1. Chapter 3

2. Temperature limits the occurrence of life. • most life processes occur within the temperature range of liquid water, 0o-100oC • few living things survive temperatures in excess of 45oC • freezing is generally harmful to cells and tissues

3. Tolerance of Heat • Most life processes are dependent on water in its liquid state (0-100oC). • Typical upper limit for plants and animals is 45oC (some cyanobacteria survive to 75oC and some archaebacteria survive to 110oC). • Good: high temp -> organisms develop quicker • The bad: High temperatures: • denature proteins • accelerate chemical processes • affect properties of lipids (including membranes)

4. Oxygen consumption increases as a function of temperature

5. Metabolic theory of ecology • Temperature has consistent effects on a range of processes important to ecology and evolution (Univ of New Mexico ecologists) • Rates of metabolism • Rates of development of individuals • Productivity of ecosystems • Rates of genetic mutation • Rates of evolutionary change • Rates of species formation

6. What about freezing temperatures?

7. Freezing temperatures… • Temperatures rarely exceed 50 degrees C (except….) • Temperatures below freezing point of water are common • On land • In small ponds which may become solid during winter • So: adaptation is necessary

8. Tolerance of Freezing • Freezing disrupts life processes and ice crystals can damage delicate cell structures. • Adaptations among organisms vary: • maintain internal temperature well above freezing • activate mechanisms that resist freezing • glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution) • glycoproteins can also impede the development of ice crystals, permitting “supercooling” • activate mechanisms that tolerate freezing

9. Pure water: freezes at 0 degrees C • Seawater: freezes at -1.9 degrees C • Contains about 3.5% dissolved salts

10. Glycoproteins act as a biological antifreeze in the antarcticcodthe fish’s blood and tissues don’t freeze due to the accumulation of high concentrations of glycoproteins, which lower its freezing point to below the min temp of seawater (-1.8C) and prevent ice crystal formation

11. supercooling • Another physical solution to freezing • is the process of lowering the temperature of a liquid or gas below its freezing point w/o it becoming a solid • Liquids can cool below the freezing point w/o ice crystals development • Ice generally forms around some object (a seed) • In a seed’s absence, pure water may cool more than 20C below its freezing point w/o freezing • Recorded to -8C in reptiles and to -18 in invertebrates • Glycoproteins in the blood impede ice formation by coating developing crystals

12. Each organism functions best… …under a restricted range of temperatures (but of course!) Optimum: narrow range of environmental conditions to which organism x is best suited Temperature! One such example. Put a tropical fish in cold water and it becomes sluggish and soon dies; put an Antarctic fish in temperatures warmer than -5C, and it won’t tolerate it but Many fish species from cold environments swim as actively as fish from the tropics

13. Enzymes and temperatures and swimming • Different temperatures result in different enzyme formation (in quantity or in qualitative difference of the enzyme itself) • Rainbow trout: • Low temp in its native habitat during the winter • Higher temp in the summer

14. Compensation is possible. • Many organisms accommodate to predictable environmental changes through their ability to “tailor” various attributes to prevailing conditions: • rainbow trout are capable of producing two forms of the enzyme, acetylcholine esterase: • winter form has highest substrate affinity between 0 and 10oC • summer form has highest substrate affinity between 15 and 20oC

16. The thermal environment includes numerous avenues for heat gain and heat loss

17. Pathways of heat exchange

18. Thermal image of Canada geese on a cold day

19. What you eat… The heat, water, food and salt budgets of animals (including us) are coupled by diet, evaporative water loss and excretion

21. Keeping cool • Although few animals sweat the way that we do, all lose heat by evaporation from their respiratory surfaces • When water is scarce…stay out of the sun • Why then do several species of seabirds nest in full sun on bare sand, while wedge-tailed shearwater builds it nests under-sand? • Sooty terns can tolerate a hot nesting environment

22. Why? • Theories? • Predators?

23. Hatching success of wedge-tailed shearwaters is highly dependent on the thermal environment

24. Why? • Diets and feeding regimes • Sooty Terns feed on fish and squid – close to the nesting sites; male and female cooperation in incubation duty • Shearwaters, similar diet, but feed hundreds of km from their nesting sites • So: • Sooty terns have stomach full of water-laden food  water for evaporative heat loss (remember: fish provide supply of free water) • Shearwaters  plenty of fat for fast but little water (fat has less water than fresh fish)

25. The greenhouse effect

28. Carbon dioxide concentrations in the atmosphere – measured at Hawaii

30. Homework assignment #2 • Use scientific literature (what is that?) • Read 1 article (no older than 2007) on the issue of: impact of climate change. • Send me the article for approval by March 10 • Summarize the article. • Grammar. Reference. Logic. Etc. no cut and paste. • Email me the summary. • Present the material during class (5-7 min) • Due: March 25 (PDHP). • No late papers accepted.

31. Homeothermy increases metabolic rate and efficiency

32. Organisms maintain a constant internal environment. • An organism’s ability to maintain constant internal conditions in the face of a varying environment is called homeostasis: • homeostatic systems consist of sensors, effectors, and a condition maintained constant • all homeostatic systems employ negative feedback -- when the system deviates from set point, various responses are activated to return system to set point

33. Negative feedback system

34. Temperature Regulation: an Example of Homeostasis • Principal classes of regulation: • homeotherms (warm-blooded animals) - maintain relatively constant internal temperatures • poikilotherms (cold-blooded animals) - tend to conform to external temperatures • some poikilotherms can regulate internal temperatures behaviorally, and are thus considered ectotherms, while homeotherms are endotherms

35. Homeostasis is costly. • As the difference between internal and external conditions increases, the cost of maintaining constant internal conditions increases dramatically: • in homeotherms, the metabolic rate required to maintain temperature is directly proportional to the difference between ambient and internal temperatures

36. Limits to Homeothermy • Homeotherms are limited in the extent to which they can maintain conditions different from those in their surroundings: • beyond some level of difference between ambient and internal, organism’s capacity to return internal conditions to norm is exceeded • available energy may also be limiting, because regulation requires substantial energy output

37. Partial Homeostasis • Some animals (and plants!) may only be homeothermic at certain times or in certain tissues… • pythons maintain high temperatures when incubating eggs • large fish may warm muscles or brain • some moths and bees undergo pre-flight warm-up • hummingbirds may reduce body temperature at night (torpor)

38. Hummingbirds maintain a constant low body temp when in torpor

39. Countercurrent heat exchange

40. Delivering Oxygen to Tissues • Oxidative metabolism releases energy. • Low O2 may thus limit metabolic activity: • animals have arrived at various means of delivering O2 to tissues: • tiny aquatic organisms (<2 mm) may rely on diffusive transport of O2 • insects use tracheae to deliver O2 • other animals have blood circulatory systems that employ proteins (e.g., hemoglobin) to bind oxygen

41. Countercurrent Circulation • Opposing fluxes of fluids can lead to efficient transfer of heat and substances: • countercurrent circulation offsets tendency for equilibration (and stagnation) • some examples: • in gills of fish, fluxes of blood and water are opposed, ensuring large O2 gradient and thus rapid flux of O2 into blood across entire gill structure • similar arrangement of air and blood flow in the lungs of birds supports high rate of O2 delivery

42. Conservation and Countercurrents • Countercurrent fluxes can also assist in conservation of heat; here are two examples: • birds of cold regions conserve heat through countercurrent circulation of blood in legs • warm arterial blood moves toward feet • cooler venous blood returns to body core • heat from arterial blood transferred to venous blood returns to core instead of being lost to environment • kangaroo rats use countercurrent process to reduce loss of moisture in exhaled air

43. A fish’s gill is designed to promote countercurrent circulation of blood and water

44. Skin temperatures of the leg and foot of a gull standing on ice show that heat is retained in the body