BIOB34 Module 3

Page 1: Overview of Thermal Physiology

• Thermal energy influences chemical interactions and biochemical reactions

• Thermal strategy includes behavioral, biochemical, and physiological responses

• Ambient temperature is the most important environmental influence on an animal's thermal strategy

Page 2: Thermal Strategies

• Two major thermal strategies: tolerance and regulation

• Tolerance allows body temperature to vary with ambient temperature

• Regulation maintains a constant body temperature regardless of ambient temperature

• Both strategies have costs and benefits

Page 3: Heat Fluxes

• Body temperature reflects the thermal energy of molecules in the body

• Thermal energy can move from the animal to the environment or vice versa

• Thermal energy moves "down" a temperature gradient

• There are many sources and sinks of thermal energy

Page 4: Heat Fluxes

• Total thermal energy is a dynamic thing

• Some tissues can generate heat, while others can dissipate heat

• Heat loss depends on specific factors such as evaporation and conduction

Page 5: Types of heat flux

• Convection is the transfer of thermal energy between an object and a moving external medium

• Rate of heat exchange depends on thermal gradient, fluid flow rate, and fluid conductivity

• Radiation is the emission of electromagnetic radiation, with the sun being the most important source

• Basking and darker colors enhance heat absorption

Page 6: Types of heat flux

• Evaporation occurs when water molecules absorb thermal energy and transition from liquid to vapor

• Evaporative cooling depends on the volume of water and heat of vaporization

• Salt increases the heat of vaporization

Page 7: Types of heat flux

• Conduction is the transfer of thermal energy from one object or fluid to another

• Heat flux is the rate of heat transfer from hotter to colder

• Units for heat flux should be negative

Page 8: Fourier's Law: quantifying thermal conduction

• Fourier's Law equation: Q = kA∆T/d

• Q is the rate of heat flow, k is thermal conductivity, ∆T is temperature gradient, and d is distance of flux

• Thermal conductivity varies with material type and geometry

Page 9: Fourier's Law: quantifying thermal conduction

• Guard hairs, underfur, darkly pigmented skin, blubber/fat layer are examples of thermal conduction in animals

• Distance of flux affects the transfer of heat from source to sink

• Winter coats help animals keep warm

Page 10: Conduction

• Thermal conductivity varies with the type of material

• Water has very high thermal conductivity

Page 11: Insulation

• Insulation reduces thermal exchange

• Internal insulation includes blubber, while external insulation includes hair, feathers, air, and water

• The effectiveness of insulation depends largely on its thickness

Page 12:

• Surface Area to Volume Ratio

  • Influences all aspects of heat exchange

  • Large animals exchange heat more slowly than small animals

  • Bergmann’s rule

    • Animals living in cold environments tend to be larger

  • Allen’s rule

    • Animals in colder climates have smaller extremities

  • Behavioural adjustments

    • Body posture can alter exposed surface area

    • Huddling behavior reduces effective surface area

Page 13:

• Thermal Strategies

  • Relative stability of body temperature

  • Poikilotherm

    • Variable body temperature

  • Homeotherm

    • Stable body temperature

Page 14:

• Thermal Strategies

  • Source of thermal energy

    • Ectotherm

      • Environment determines body temperature

    • Endotherm

      • Animal generates internal heat to maintain body temperature

      • Most animals best described by a combination of terms

Page 15:

• Temporal and Regional Endothermy

  • Hypometabolic phase accompanied by a decrease in body temperature

  • E.g. hibernation, torpor

  • Metabolic energy that would normally be used for thermoregulation is saved

  • Time course differs among animals and types of dormancy

  • Torpor: usually less than a day

  • Hibernation/estivation: longer

Page 16:

• Homeothermy is relative

  • Circadian rhythm evident in:

    • Metabolic rate

    • Body temperature

Page 17:

• (Remote) Data loggers

  • Implantable

  • Sub-cutaneous

  • Attached to skin

Page 18:

• Homeothermy is relative

  • Animal breeding is big business

  • Important to know when fertilization is possible

  • Can be tracked in hormones

  • Solution: Easier way of tracking fertility

  • Metabolic rate and body temperature vary with reproduction cycle

Page 19:

• Homeothermy is relative

  • Solution: Easier way of tracking fertility

  • Metabolic rate and body temperature vary with reproduction cycle

Page 20:

• Measuring temperature

  • Best option is in-ear scan

  • Can hold an animal more comfortably

  • Capturing is a more accurate method

  • Can broadcast a digital signal

Page 22:

• Some subjects are "willing" participants

  • Natural Cycles "The only FDA Cleared birth control app"

  • Helps understand thermal reproduction

  • Population and biology

Page 23:

• Body temperature varies with reproductive status in a large mammal

  • Data for larger research

  • Increase during ovulation

  • Animal tissues can get larger

  • Reproduction arresting

Page 24:

• Homeothermy is relative

  • Circadian rhythm affects in Humans

  • Same in all genders

Page 25:

• Homeothermy is relative

  • Mean daily body temp range (°C)

  • Mean daily body temp (°C)

  • Relationship between body size and the magnitude of daily fluctuations in temperature

Page 26:

• Homeotherm response to temperature variation

  • Consider treeshrews

  • Native to Borneo

  • Thermoregulatory parameters of Tupaia minor measured during the rest phase of the activity cycle

Page 27:

• Thermal Zones of Homeotherms

  • Thermoneutral zone

    • Optimal range for physiological processes; metabolic rate is minimal

  • Upper critical temperature (UCT)

    • Metabolic rate increases as animal induces a physiological response to prevent overheating

  • Lower critical temperature (LCT)

    • Metabolic rate increases to increase heat production

  • Animals differ in the width of their thermoneutral zone, UCT, and LCT

Page 28:

• Thermal Zones of Homeotherms

  • Total sum of heat loss rate is radiation, conduction, convection

Page 29:

• Homeotherm response to temperature variation

• Variation in TNZ breadth

• Pygmy treeshrew Tupaia minor ~ 65 g

• Large treeshrew Tupaia tana ~ 250 g

• Danielle Levesque Univ. of Maine

Page 30:

• Homeotherm response to temperature variation

• Variation in TNZ breadth

• Pygmy treeshrew Tupaia minor ~ 65 g

• Large treeshrew Tupaia tana ~ 250 g

• Danielle Levesque Univ. of Maine

• Figure 2. Width of the thermoneutral zone (TNZ) and the basal metabolic rate (BMR) of a number of mammal species.

• Treeshrews from Borneo (Tupaia minor and Tupaia tana) are represented by blue squares; other scandentians are represented by yellow triangles.

• The dashed lines are the regression lines determined using ordinary least squares, and the solid black lines are the regression lines determined using phylogenetic generalized least squares (pgls; see text).

• The gray lines show the 95% confidence intervals of the pgls analysis.

• All BMR data from Genoud et al. (2017) were used to calculate the confidence intervals, but only species less than 1 kg are shown for visual clarity.

• noscares statistican significantly argather than positive relationship between body mass breathe or thermal neutral zone easiertothem

Page 31:

• Thermal Tolerance of Poikilotherms

• Poikilotherms do not have a thermoneutral zone, UCT, or LCT

• Preferred temperature

• Ambient temperature for optimal physiological function

• Incipient lethal temperature

• Ambient temperature at which 50% of animals die

• Incipient upper lethal temperature (IULT)

• Incipient lower lethal temperature (ILLT)

• Range of tolerance

• Range of ambient temperatures between IULT and ILLT

• somewilldielessorhighertemperature

• Higher tower

Page 32:

• Thermal Tolerance of Animals

• Eurytherm

• Can tolerate a wide range of ambient temperatures

• Stenotherm

• Can tolerate only a narrow range of ambient temperatures

• Eurytherms can occupy a greater number of thermal niches than stenotherms

• magnitude may vary based on animal nine less range in differentemeanin lower variation in temperature

Page 33:

• Temporal and Regional Endothermy

• Regional heterotherms

• Body temperature varies in regions of the body

• Billfish heater organs near eyes

• warmer bodies in sea are larger

• move their enough thermal anana don't eyes around easily if they won tissue to act need increase an they us catcycling bunriss swim in high speed exist in widerange orianaitude active visual hunter so can survive in high range of temperature

• Games consume an can't feel when responding activity itivititis related pumping restore to temp can generate meat and keep eyes warm efficient for vision for hunting

Page 34:

• Thermogenesis by Ion Pumping

• Ion gradients degrade for two main reasons

• Membrane proteins use electrochemical energy to drive transport and biosynthesis

• Ions leak across membranes

• Ions must be continually pumped

• Ion-pumping membrane proteins produce heat

• E.g. Billfish heater organs (modified muscles that don't contract)

• Plasma membranes of endotherms are leakier than those of ectotherms

• Increased thermogenesis due to ion pumping

• axondrive actionpotential

Page 35:

• Temporal and Regional Endothermy

• Regional heterotherms

• Body temperature varies in regions of the body

• Billfish heater organs near eyes

• Tuna retain heat in red muscle

• Mackerel Tuna orsumon a winter whitefibres deeper comparedtotuna anaintheirredfibre theygenerateneat

Page 36:

• Temporal and Regional Endothermy

• Regional heterotherms

• Body temperature varies in regions of the body

• Billfish heater organs near eyes

• Tuna retain heat in red muscle

Page 37:

• Temporal and Regional Endothermy

• Regional heterotherms

• Body temperature varies in regions of the body

• Billfish with heater organs near eyes

• Tuna retain heat in red muscle

• The thorax of some flying insects men m' Ineadmseives constantly several degrees above abdomen amingtowarmenraap awinantostinwarm rainactivates metnorax

Page 38:

• Heat Production in Insects Prior to Flight

• Mechanisms:

• Carbohydrate metabolism in flight muscles

• Futile cycling: 2 opposing enzymes are activated simultaneously

• Antagonistic flight muscles contract simultaneously

• Energy is expended and heat is produced without movement

• Not uncoordinated, like in shivering

• Wing movement

• Frequency and orientation of the wings are controlled to avoid generating lift – wing buzzing

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Page 39:

• Temperature effects: Biochemistry and Physiology

• Proteins and lipids are affected by temperature over the normal range encountered by animals

• Hydrogen bonds and van der Walls forces are disrupted by high temperature

• Hydrophobic interactions are stabilized at high temperatures

• musical forces are disrupted someme are changing differently with temp

Page 40:

• Macromolecule Structure

• Proteins and lipids are affected by temperature over the normal range encountered by animals

• Hydrogen bonds and van der Walls forces are disrupted by high temperature

• Hydrophobic interactions are stabilized at high temperatures

• Show JOVE video on membrane fluidity

Page 41:

• Membrane Fluidity

• Membrane fluidity is affected by temperature

• Low temperatures cause membrane lipids to solidify

• High temperatures increase membrane fluidity

• Changes in membrane fluidity affect protein movement and membrane function

• Increased protein movement with increased fluidity

• tooraid membrane burstopen anisotropy amembraneenacaneroneinenvironment enatisnestfitted a idealorandity witntemperature tepidity fludity

Page 42:

• Homeoviscous Adaptation

• Homeoviscous adaptation

• Maintain membrane fluidity at different temperatures by changing membrane lipids, cholesterol content

• Mechanisms of homeoviscous adaptation

• Fatty acid chain length

• Shorter chains increase fluidity

• Saturation

• More double bonds increase fluidity

• maintainsimilar visoriturnaityairing rangesortemperature onename anytime

Page 43:

• Homeoviscous Adaptation

• Mechanisms of homeoviscous adaptation, cont.

• Phospholipid classes

• Phosphatidylcholine (PC): decrease fluidity

• Phosphatidylethanolamine (PE): increase fluidity

• Cholesterol content

• Prevents solidifying when the membrane is cooled

Page 44:

• Thermal adaptation, acclimation, acclimatization

• Ectotherms remodel tissues in response to long-term changes in temperature

• Quantitative strategy

• More metabolic "machinery"

• For example, increase the number of muscle mitochondria in low temp

• Qualitative strategy

• Alter the type of metabolic "machinery"

• For example, different myosin isoforms in winter and summer

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Page 45:

• Thermal adaptation: LDH enzyme in killifish

• Patricia Schulte UBC Fellow RSC Common killifish (Fundulus heteroclitus)

• Small, coastal (estuarine) fish

• Found along Atlantic Coast

• Northern populations can experience avg. temp 10°C > Southern populations

• LDH-B subunit

• Two alleles, distinct expression among N-S pops.

Page 46

• Swimming performance in relation to temperature differs among populations of common killifish (Fundulus heteroclitus)

  • This pattern makes sense given the difference in 'normal' temperatures experienced

• Ucrit (max. sustainable swim speed) is used to measure swimming performance

Page 47

• LDH alleles in common killifish exhibit enzyme activity in relation to temperature

• Enzyme activity underpins the difference in performance among populations

Page 48

• Cold adaptation in psychrotrophs (animals that thrive at low temperatures)

• Protein "breathing" refers to changes in 3-D shape during the catalytic cycle

• Enzymes do not breathe well at low temperatures because weak bonds are strengthened

• Decreased enzyme efficiency at low temperatures

• Psychrotrophs possess cold-adapted enzymes with fewer weak bonds

• Cold-adapted enzymes are more vulnerable to temperature-dependent unfolding

Page 49

• Strategies for surviving freezing temperatures

• Freeze-tolerance: animals allow their tissues to freeze in a controlled, safer way

• Freeze-avoidance: animals use behavioral and physiological mechanisms to prevent ice crystal formation

Page 50

• Supercooling: water can remain liquid below 0°C in the absence of a nucleator

• Ice crystal formation requires a trigger such as a cluster of water molecules or a macromolecule acting as a nucleator

• Deleterious effects of ice crystal formation include piercing membranes and increasing osmolarity

Page 51

• Freeze-avoidance: solutes depress the freezing point of a liquid

• Antifreeze macromolecules disrupt ice crystal formation by binding to small ice crystals and preventing growth

Page 52

• Freeze-tolerance: two mechanisms

  • Producing nucleators outside of the cell

  • Controlling the location and kinetics of ice crystal growth

• Extracellular fluid freezes, but intracellular fluid remains liquid

• Intracellular solutes are produced