For a foraging bumblebee, warming the thorax to a high temperature is critical

Thermal relations

• Heat transfer between animals and their environments– Behavior– Autonomic mechanisms- accelerated

metabolism of enery reserves– Adaptive mechanisms-- acclimationzation

Heat transfer

• Heat transfer depends on 3 factors

• Surface area– small vs large animals

• Temperature difference between body (Tb) and ambient (Ta)

• Special heat conductance of the animal’s surface (amount of insulation)

Heat transfer

• Heat transfer depends on 3 factors

• Surface area– small vs large animals

• Temperature difference between body (Tb) and ambient (Ta)

• Special heat conductance of the animal’s surface (amount of insulation)

Figure 8.4 A model of an animal’s body showing key temperatures

Figure 8.2 Eastern phoebes overwinter where avg. minimum air temp. in Jan. is –4°C or warmer

Heat exchange

• All organism exchanges heat with its environment by

• Conduction

• Convection

• Radiation

• Evaporation

Figure 8.3 An animal exchanges heat with its environment

Figure 8.6 A bird loses heat in net fashion to tree trunks as it flies past them on a cold winter night

Thermal tolerance

• Thermal tolerance- phylogenetic differences in thermal tolerance– Reflected in geographical distributions

• Seasonal changes in thermal tolerance- photoperiod

• Limit of temperature tolerance• O2 plays an important role in speed of

adaptation• MR change

Temperature classifications of animals

• Base on body heat

• Ectothermic

• Heat exchange with environment more important

• Low MR

• High thermal conductance– poor insulation

• Behavior-- thermoregulation

Adaptation to cold environment– freeze tolerant vs freeze intolerant

• Freeze intolerant– Solutes lowering freezing point– Glycerol – high concentration in overwintering

insects• Lower supercooling point-avoid ice crystal

formation• Protective action against freezing damage

– Antifreeze substance in blood

Freeze tolerant animals

• Intertidal areas– survive extensive ice formation within body– Nucleating agents (protein)– Aids in ice formation-found in hemolymph– Increase in blood glucose level

• Shivering

• Change in blood flow to skin

Figure 8.1 Four categories of animal thermal relations based on endothermy and thermoregulation

Figure 8.10 Acclimation of metabolic rate to temperature in a poikilotherm

Temperature acclimation

• Cells may increase the production of certain enzymes– Compensate for lowered activity of certain

enzymes– Enzymes with same function but different

temperature optima

• Membrane may change in proportions of saturated/unsaturated lipids

• Body size

Figure 8.11 Compensation through acclimation (Part 1)

Figure 8.16 Enzyme adaptation in four species of barracudas

Figure 8.17 An enzyme very sensitive to temperature change-brain acetylcholinersterase for Ach in polar afish

Figure 8.18 The fluidity of lipid-bilayer membranes from brain tissue (Part 1)

Figure 8.18 The fluidity of lipid-bilayer membranes from brain tissue (Part 2)

Figure 8.19 The process of extracellular freezing in a tissue

Figure 8.20 Seasonal changes in antifreeze protection in winter flounder (Part 1)

Figure 8.20 Seasonal changes in antifreeze protection in winter flounder (Part 2)

Summary – poikilothermy part 1

• Ectotherms– Determined by equilibrium with Ta– Behavioral– BMR usually low

• When acclimated to low temperature– Common response- partial compensation

• Return MR toward the level that prevailed prior to the change

Summary – poikilothermy part 2

• Long evolutionary histories of living at different Tb– Physiological differences evolved– Important mechanisms of adaptation

• Molecular specialization• Synthesize different homologs of protein molecules• Different suites of cell-membrane phospholipids

• When exposed to heat – heat-shock proteins– Guide reversibly denatured proteins back into correct

molecular conformation

Summary – poikilothermy part 3

• Freeze tolerant poikilotherms– Limited to extracellular body fluids

• Freeze intolerant– Behavioral avoidance– Antifreeze, glycerol

• Stabilization of supercooling – Animals remain unfrozen while at

temperatures below their freezing points

Figure 8.22 Resting metabolic rate and ambient temperature in mammals and birds (Part 1)

Box 8.1 Relation between set point and body temperature during a fever

endothermic

• Generate heat on their own• Relative constant Tb

– High MR- needs large quantity of food and water

– Surface area/volume ratio- lose heat faster

• Vasodilation and vasoconstriction• Cooling by evaporation

– Sweat/saliva

• Behavioral responses

Ectothermy

• Three responses: – Acute– Chronic– Evolutionary changes

• In high temperature– heat-shocked protein

• Freezing temperature

Homeothermy in mammals and birds

• MR increases in both cold and hot environments

• Insulation modulated by adjustments of pelage, plumage, blood flow, and posture

• Shivering and non-shivering thermogenesis (brown fat)

• Counter-current heat exchange

• Hibernation, torpor, or related processes

Figure 8.23 Metabolic rate and ambient temperature in and below the thermoneutral zone (Part 1)

Figure 8.23 Metabolic rate and ambient temperature in and below the thermoneutral zone (Part 2)

Figure 8.24 Gular fluttering is one means of actively increasing the rate of evaporative cooling

Figure 8.25 The deposits of brown adipose tissue in newborn rabbits

Figure 8.26 Regional heterothermy in Alaskan mammals

Figure 8.28 Heat loss across appendages is sometimes modulated in ways that aid thermoregulation

Figure 8.29 Blood flow with and without countercurrent heat exchange

Figure 8.30 Countercurrent heat exchange short-circuits the flow of heat in an appendage

Figure 8.31 Structures hypothesized to be responsible for cooling the brain in artiodactyls

Figure 8.32 Breathing patterns limit hyperventilation of respiratory-exchange membranes in panting

Figure 8.34 Seasonal acclimatization in two species of mammals (Part 2)

Figure 8.35 Mammalian physiological specialization to different climates

Figure 8.36 Changes in body temperature during hibernation

Figure 8.37 Changes in metabolic rate during daily torpor

Figure 8.38 Energy savings depend on temperature

Figure 8.39 Cross section of a tuna showing nature of blood supply to red swimming muscles

Figure 8.40 Red-muscle temperatures of tunas at various ambient water temperatures

Figure 8.44 Effect of air temperature on wing-beat frequency & metabolic rate in flying honeybees

Temperature acclimation

• Cells may increase the production of certain enzymes– Compensate for lowered activity of certain

enzymes– Enzymes with same function but different

temperature optima

• Membrane may change in proportions of saturated/unsaturated lipids

• Body size