Temperature

1. Temperature Response to Temperature Stress

2. Outline (1) Endothermy in Mammals (2) Response to Heat Stress (3) Response to Cold

5. Geographic Distribution of species is determined, in part, by temperature

6. How do organisms deal with Temperature Stress?

7. Temperature • Affects the rates of biochemical reactions, and of physical processes (diffusion, osmosis) • Protein conformation and enzyme function • Affects metabolic rate

8. Body Temperature • Poikilotherm: body temperature is variable • Homeotherm: body temperature is constant • Ectotherm: regulate body temperature externally (behavior); most are poikilotherms • Endotherm: elevated body temperature using metabolic heat (mammals, birds, tuna, some insects); many are homeotherms

9. Variation in Body Temperature °C EctothermsEndotherms Marine Deep Sea fish 4-6 Whale 36 Frog 22-28 Human 37 Housefly 30-33 Rodent 35-37 Tropical fish 20-28 Bat 35-39 Desert Iguana 36-41 Chicken 40 Dove 39-42 Bee 35-42

10. Evolution of Body Temperature • Why are endotherms 35-40°C? • Many ectotherms aim for these temperatures as well • Optimal for enzyme activity • Faster neuronal, hormonal function • Slight elevation: Easier to gain than lose heat • Physical properties of water are at an ideal balance of viscosity, specific heat, and ionization

11. Endothermy Buffers biochemical reactions against temperature stress Allows organisms to invade a broader range of habitats

13. Thermoregulation: evolutionary causes? Evolved independently multiple times WHY? Two Hypotheses: Thermoregulatory Advantage • Maintain constant body temperature • Easier to maintain a high body T than lower Aerobic Capacity Advantage • Selection for enhanced physical performance (endurance, locomotion) • With increased heat production as a secondary effect

14. Endothermy All animals produce heat, but endotherms produce more (4-8 times) Metabolic rate is ~4-10 times higher Largest component of energy budget

15. Where and How is Body Heat Produced?

16. How is Body Heat Produced? All Metabolic Activity produces Heat • ATP-producing reactions • ATP-consuming reactions • Ion pumping (ATP hydrolysis) (~25%) • Mitochondrial proton leak • Urea production (~2%) • Glycolysis (~5%) • Etc Mostly in the mitochondria 3/4 in abdominal organs (brain, gut, liver, kidney, heart, lungs) some in muscles

17. Cytochrome oxidase activity Mitochondrial Surface Area Lizard 100% 100% Mouse 50% 50% Liver Liver Heart Heart Brain Brain Kidney Kidney

18. So heat production is directly linked to metabolism… • And also oxygen consumption and food intake

19. Mechanism of heat production through mitochondrial proton leak

20. Typically, the Electron transport chain and oxidative phosphorylation (ATP production) is coupled. When they are not, the energy released by electron transport is released as heat, rather than used to make ATP

21. ATP Synthase

22. In specialized cells of Endotherms, protons leak across the membrane through uncoupling protein 1 (UCP1 = thermogenin) Such proton diffusion generates heat

23. Box 6.1, p. 220 This uncoupled reaction occurs to a high degree in brown adipose tissue, which has large numbers of large mitochondria Cold --> release Norepinephrine Hydrolyzes triacylglycerols in BAT (Brown Adipose Tissue) cells to release fuels for mitochondrial oxidation Lipid oxidation proceeds with UCP1 activated

24. Nonshivering thermogenesis Increase rate of oxidation of stored lipids Uncoupling of oxidative phosphorylation from electron transport in the mitochondria Allows energy to be released as heat rather than stored as ATP More prominent in cold-adapted mammals, hibernators, newborns

25. Response to High Temperature Stress

26. Last time we discussed the structure and function of enzymes, which are proteins • Protein folding depends on thermodynamics, and can be disrupted by high temperatures • How is protein structure and function maintained under conditions of temperature (or other) stresses?

27. Heat Shock Proteins Hsp70 Ensure correct protein folding Not only used for temperature stress, but also other stresses (osmotic shock, etc) Figure: silver staining of Hsps in the cell

28. Hsp70

29. The fruit fly, Drosophila melanogaster lay their eggs on rotting fruit • The larvae can experience very high temperatures while growing on the fruit • They use the enzyme alcohol dehydrogenase (ADH) to break down alcohol that accumulates in the rotting fruit • They need to protect their proteins and enzymes such as ADH against denaturing under heat stress

31. Inserting extra copies of Hsp 70 enhanced tolerance of high temperature in Drosophila melanogaster Extra copy strain: 12 copies Excision strain: 10 copies Number of copies affects the degree of hsp expression (the amount of hsp transcribed)

32. Evolutionary tradeoffs of high Hsp expression? Cost to growth: Constant (constitutive) expression of hsp inhibits cell proliferation (would inhibit growth) Cost to Reproduction: decreases rates of age-specific mortality during normal aging, while maternally experienced heat shock depresses the production of mature progeny (Silbermann and Tatar 2000)

33. Temperatures at which HSPs are induced have evolved to correspond to temperatures that are stressful for a given species or cell type. • Antarctic organisms begin to express HSPs at relatively low temperatures (< 10°C)(Vayda and Yuan 1994) • Some hyperthermophiles do not express HSPs until temperatures exceed 60°C(Trent, Osipiuk et al. 1990; Ohta, Honda et al. 1993; Polla, Kantengwa et al. 1993; Trent, Gabrielsen et al. 1994) • Hypothermic regions of mammals (e.g., testis) express HSPs at lower temperatures than normothermic organs(Sarge 1995; Sarge, Bray et al. 1995)

34. Canalization(flip side of plasticity) • Influenced by developmental stability • Stress could disrupt canalization and lead to new phenotypes • Particular genes might be important for maintaining developmental stability and buffer against perturbations

35. Queitsch et al. 2002. Nature. 417:618-624

36. A potential “plasticity gene”in response to environmentalstress • Heat-shock protein 90 (Hsp 90) chaperones the maturation of many regulatory proteins • In Drosophila melanogaster, buffers genetic variation in morphogenetic pathways • Reducing Hsp90 function in Drosophila or Arabidopsis produces an array of morphological phenotypes, revealing hidden genetic variation

37. Development abnormalities in HSP90 deficient Drosophila (Rutherford and Lindquist. 1998. Nature) Study criticized because fitness consequences were not examined

38. Normal Hsp90 inhibited

39. Normal Unlike case of Drosophila, diverse phenotypes here were not “monstrous” but potentially adaptive Dependence on Hsp90 for developmental stability varied Hsp90 inhibited

40. Potential Mechanism: • Under stress, Hsp90 is recruited to maintain protein folding and the function of proteins • Ability to maintain developmental pathway is exceeded

41. Adaptation to Cold

42. Differences between Aquatic Vertebrates vs Invertebrates???

43. Because of their Freshwater originand osmotic properties, cold temperatures pose problems for fishes

44. Cold temperatures pose problems for fish in water because they are hyposmotic • Freezing point is higher in their extracellular fluids relative to ambient seawater

46. Osmotic/Temperature Interactions • Freshwater Freezes at 0°C • Seawater Freezes at -1.89°C • But hyposmotic fish might freeze at -0.7°C

47. Solutions • Cold water fish have more NaCl in extracellular fluids • Uses osmolytes such as glycerol (works better than NaCl) • Antifreeze proteins

48. Antifreeze proteins • 200x more effective than NaCl • Not freeze until -6°C • Hot commodity these days (cryopreservation, food preservation, health)

49. Antarctic FishPagothenia borchgrevinki

50. Molecular structure of an antifreeze glycoprotein Some are multigene families that have experienced multiple gene duplications