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Lecture 5: Thermoregulation and Resting Metabolism

Lecture 5: Thermoregulation and Resting Metabolism. Ectotherm - organism that relies on external sources of heat

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Lecture 5: Thermoregulation and Resting Metabolism

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  1. Lecture 5: • Thermoregulation and Resting Metabolism

  2. Ectotherm - organism that relies on external sources of heat Endotherm - organism that produces enough heat by its own metabolic processes to affect its own body temperature; can increase metabolic rate in response to reduced ambient temperature Poikilotherm - organism that experiences variable body temperature, often closely tracking ambient temperature Homeotherm - organism that experiences (relatively) constant body temperature (e.g., + 2 C)

  3. Fig. 17-9 Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.

  4. Endotherm Tb and Metabolic Rate vs. Ambient Temperature Note:slight typo in figure, TNZ goes from LCT to UCT Summit metabolism Thermal conductance (e.g., evaporative cooling by sweating or panting) Lower C.T. Upper C.T. Fig. 17-21 Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.

  5. Controlling Heat Loss within the TNZ Takes little energy. Vasomotor responses - regulate blood flow between the periphery and core Insulation adjustments - pilomotor muscles can raise ("fluff") or lower hairs or feathers (human "goose bumps" are a vestige of this) Postural changes - body shape or orientation affects heat exchange via radiation, conduction, convection

  6. High Insulation gives Low Conductance and vice versa Fig. 17-25 Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.

  7. Combining Terms in Thermoregulation Endothermic Homeotherm - most birds and mammals; some insects; some large fishes (tuna, sharks); brooding pythons;a few plants (example later in this lecture …)

  8. Combining Terms in Thermoregulation Ectothermic Poikilotherm - most marine invertebrates; arthropods; amphibians;fishes; "reptiles" (not a good name, with respect to phylogenetic relationships, e.g., birds are "reptiles" in the old sense of the term)

  9. Terms for Exceptions to "Rules" Inertial Homeotherm - relatively constant Tb because of large body size: e.g., some dinosaurs? Trivial Homeotherm - constant Tb because of constant environmental temperature: e.g., animals in the deep sea, by hydrothermal vents, pupfish living in thermal hot springs Heterotherm - homeotherm whose body temperature varies somewhat, either over time or regionally (regional heterothermy)

  10. Other Important Exceptions Regional Heterothermy Fig. 17-24 Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.

  11. Other Important Exceptions Regional Heterothermy Humans also do this, but not to such a degree (pun intended). Fig. 17-24 Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.

  12. Other Important Exceptions Many lizards maintain high and stable body temperatures (35-40 C) when active. Many birds and mammals, especially small ones, undergo regulated hypothermia and hypometabolism: Daily torpor in hummingbirds

  13. Other Important Exceptions Many lizards maintain high and stable body temperatures (35-40 C) when active. Many birds and mammals, especially small ones, undergo regulated hypothermia and hypometabolism: Daily torpor in hummingbirds Seasonal hibernation in small mammals and the Poorwill (only bird) http://www.earthrangers.com/wildwire/top-10/top-ten-hibernating-animals/

  14. Seasonal hibernation in the Poorwill, discovered by Dr. Edmund C. Jaeger in 1946 in the Chuckwalla Mts. of CA http://www.jaeger.ws/index.html

  15. Other Important Exceptions Many lizards maintain high and stable body temperatures (35-40 C) when active. Many birds and mammals, especially small ones, undergo regulated hypothermia and hypometabolism: Daily torpor in hummingbirds Seasonal hibernation in small mammals and the Poorwill (only bird) Seasonal estivation in response to heat and/or lack of water, e.g., round-tailed ground squirrel in Mojave desert

  16. Basal Metabolic Rate - Originally defined for human beings, used as an index of thyroid function. The "minimal" metabolic rate of an endotherm under fasting conditions,in the thermal-neutral zone,undisturbed,during its normally inactive time of 24-hour period (but for human beings is done during day). Standard Metabolic Rate - similar to BMR, but in an ectotherm at a specified temperature.

  17. What is Basal or Standard Metabolic Rate? Summation of all energy-consuming processes A high met. rate (i.e., per unit time) indicates that~ all physiological processes are working fast Can measure by heat production = direct calorimetry, e.g., by amount of ice melted Usually measured as O2 consumption = indirect calorimetry: O2 is final electron acceptor; technique works because most vertebrates use aerobic metabolism almost exclusively when resting under normal conditions.

  18. Metabolic Water Production varies with Diet Can also convert to an energy equivalent: C6H12O6 (glucose) + 6 O2 ---> 6 CO2 + 6 H2O + 2,820 kilojoules/mole of O2 Conversion factor depends on fuel being utilized (carbohydrate, fat, protein). Usually assume mixed diet and use 20.1 KJ/liter of O2 consumed. (1 calorie = 4.1868 joules) Can measure CO2 instead, but is a less reliable indicator of heat production. Measuring both allows best estimate of heat prod. But most studies just report O2 consumption.

  19. Endothermy in Plants Was discovered over 200 years ago by Lamarck! Has now been documented in 9 different families. Several hypotheses for the ecological relevance (selective importance = ultimate causation) of elevated temperatures in plants:

  20. protect flowers from freezing enhance rate of flower development provide a direct energy reward for insect pollinators increase diffusion rates of CO2 and volatilization of specific chemicals that attract pollinators enhance growth of the pollen tube assure reproductive success (seed set) achieve mimicry of mammalian faeces and carrion to attract scavengers and carrion flies

  21. Family Rafflesiaceae, Rhizanthes zippelii

  22. Distribution of Family Rafflesiaceae

  23. Patiño, S., J. Grace, and H. Bänziger. 2000. Endothermy by flowers of Rhizanthes lowii (Rafflesiaceae). Oecologia 124:149-155. • Abstract:Rhizanthes lowii (Beccari) Harms (Rafflesiaceae) is a parasitic plant that grows in the understory of the rainforest in South-East Asia. This plant does not have leaves, stems, or photosynthetic tissue and is characterised by the emission of a strong odour that attracts the natural pollinators, carrion flies. Flowers that volatilise odorous compounds and attract carrion flies, beetles and other insects ...

  24. … are often thermogenic. Here we present evidence of both thermogenesis and thermoregulation in R. lowii from microclimate and tissue temperatures … in natural conditions in Brunei, Borneo. Endothermy was detected in young and mature buds as well as in blooming flowers and even in decaying tissues 3 or more days after blooming. Tissue temperatures were maintained at 7-9 K above air temperature, in both female and male flowers, at all stages of floral development.

  25. Stopped here 22 Jan. 2013 Extra Slides Follow Started here 24 Jan. 2013

  26. As of Winter 2006 in the 174 course, Ted has more that can be added from his 161B lectures. These have confusing names, but do not seem to overlap with each other: 161B-04-Spr-L2-Eck02ch16.ppt = locomotion, UK 1989 Talk, mice on metabolic wheels, r-K continuum -- whole ppt file is expanded into these two: 161B-04-Spr-L3-Eck02ch16_Part_1.ppt 161B-04-Spr-L3-Eck02ch16_Part_2.ppt 161B-04-Spr-L4-Eck02ch17.ppt = thermoregulation, costs/benefits of endothermy

  27. Fig. 1. The energetic consequences of different ambient temperatures. Metabolism is fully governed by intrinsic factors only within a narrow zone of ambient temperatures – the thermoneutral zone (indicated by the area between the dashed lines, i.e. the lower and upper ‘critical’ temperatures) (calling these temperatures ‘critical’ may be considered misleading but this is the current nomenclature in thermal physiology). In mice, the thermoneutral zone lies at approximately 30°C. At ambient temperatures outside the thermoneutral zone, a large fraction of total energy is used for thermoregulation; already at normal animal house conditions (18–22°C), this fraction is an additional 50–100% above the basal metabolic rate. The shaded area indicates the extra metabolism required for body temperature defence. BMR, basal (or resting) metabolic rate. Oxygen consumption rates are arbitrary units. Based on data on wild-type mice published previously (Golozoubova et al., 2004). Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic studies. J Exp Biol 214:242-253.

  28. Fig. 2. The effects of exceeding the ambient temperature survival limits. Principal figure extended from data in Fig. 1. Dashed lines indicate the lower and upper temperature survival limits. TB, body temperature. Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic studies. J Exp Biol 214:242-253.

  29. Fig. 4. The effect of increased insulation on the thermoneutral zone. As seen, animals with a better insulation (a smaller slope of the line) must necessarily also obtain a broader thermoneutral zone, because the line must extrapolate to the same defended body temperature. Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic studies. J Exp Biol 214:242-253.

  30. Heterotherm - homeotherm whose body temperature varies somewhat, either over time or regionally (regional heterothermy) Trivial Homeotherm - deep sea organisms by hydrothermal vents, desert pupfish Inertial Homeotherm - experiences fairly constant TB because of large size, e.g., large dinosaurs Basal Metabolic Rate - "minimal" metabolic rate of an endotherm under fasting conditions, in the thermal-neutral zone, undisturbed, during its normally inactive time of the 24-hour period Standard Metabolic Rate - similar to BMR, but in an ectotherm at a specified temperature

  31. Some Terms from the Student Survey (plus or minus a few ...): Serves as Partial Review for Midterm 1 on Tuesday, 30 Jan. 2007 Ecology - study of relationships between organisms and their environments, including both biotic (i.e., other organisms) and abiotic (i.e., physical factors) Evolution - change; more specifically, heritable, cross-generational changes in populations of organisms Physiology - study of how organisms work

  32. Phenotype - physical characteristics of an organism resulting from gene expression modified by environmental factors Genotype - genetic material possessed by an individual organism, usually in the form of DNA Natural Selection - correlation between variation in one or more phenotypic traits and Darwinian fitness (~ lifetime reproductive success)

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