chp 9 thermal relations l.
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Chp 9 Thermal relations. Importance of Temperature. Temperature is a major factor affecting live of individuals. The ambient temperature is important in determining the animal metabolic rate  the rate of food acquisition

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Chp 9 Thermal relations

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importance of temperature
Importance of Temperature
  • Temperature is a major factor affecting live of individuals.
    • The ambient temperature is important in determining the animal metabolic rate  the rate of food acquisition
    • The animal’s tissue temperature affects the biophysical processes, the efficiency of protein function, the viscosity of the cell fluids.
  • Definitions:
    • Ectotherms: animal temperature is dictated by environmental temperature  poikilotherms because their temperature varies
    • Endotherms: animals that regulate their tissue tissue temperature
    • Homeotherms: use endogenous heat to thermoregulate
    • Heterothermy: difference in thermal realtions  temporal if difference in time (ex: hibernation) or regional (body parts)
temperature and heat
Temperature and Heat
  • Temperature: measure of the intensity of molecular movement within an object.
  • Heat: a form of energy due to the motion of the atoms forming the object. The amount of heat depends on the size of the object as well as its temperature
  • Heat moves by conduction or convection from high to low temperatures
  • The transfer of heat raises the temperature of the object receiving heat and vice versa
  • Thermal equilibrium = temperatures are the same
heat transfer between animals and their environment
Heat transfer between animals and their environment

Conduction: transfer of heat through atomic-molecular interactions by direct contact

Convection: heat transferred through macroscopic motion flow = wind

Radiation: all objects emit electromagnetic radiations which reflects against surface and warm them.

Evaporation: the transformation of water from liquid to gas use energy  loss of heat due to vaporization

heat gain and loss in nature
Heat gain and loss in nature

Radiant temperature of the sky

The sky temperature is cooler than the earth and animals  loss of energy from earth  sky

Solar radiation

High and visible in the color spectrum  heat gained by earth and animals

poikilothermy ectothermy
Poikilothermy - Ectothermy
  • Most common: all invertebrates and many vertebrates  animal’s body temperature varies with the environment.
  • Terrestrial animals have the possibility to adjust their body temperature with behavior pattern (basking in the sun, resting underground..)  behavior thermoregulation if body temperature is fairly constant
    • Eurythermal: can function over a wide range of temp
    • Stenothermal: function in a narrow range of temperature
physiological responses in poikilotherms
Physiological responses in poikilotherms

Acute response: rapid changes in metabolic rate  follows an exponential function of body temperature

Factor by which the MR increase when body temperature increase by 10 = temperature coefficient Q10

Q10= Rt/R(t-10)

Around 2-3 for poikilotherms

physiological responses in poikilotherms11
Physiological responses in poikilotherms

Chronic response: Exposure to different temperature will induce different metabolic response  acclimation

Initial response is a drop in metabolism

Followed by an increase  compensation

Acclimation is due to a change in the number and activities of enzymes involved in metabolism.

homeothermy in mammals and birds
Core body temperature fairly constant

Require regulation  brain involvement

Basal metabolic rate in these species is the metabolism rate when the animal is resting, fasting and at thermoneutral zone (TNZ)

Metabolic rate increases in both cold and hot environments


Homeothermy in Mammals and Birds
Varies with species

Some mouse species have a TNZ of 30-35oC

Eskimo dogs: - 25oC to 30oC

thermoregulation basis
Often, the external temperatures are lower than the animal’s core body temp  animal needs to energy to increase body temp

The rate of loss varies with the animals: M = C(TB-TA )

C characterizes the animal’s ability to loose heat

If I=1/C, I = insulation = measure an animal overall resistance to loose heat

Main factors affecting I:




Thermoregulation: basis
temperatures below thermoneutrality
A) the cooler the temperature, the higher the metabolic rate

B) however, near the TNZ the metabolism does not fall to 0 but reach BMR

The slope of the line is directly related to the level of insulation present in the animal

Temperatures below thermoneutrality
Pelage: pilomotor response

Plumage: pilomotor response

Blood flow: vasoconstriction/dilation


heat production


Non shivering thermogenesis  brown adipose tissue = brown fat

Heat production
mammals and birds in hot environments
Behavorial defenses


Body reactions such as panting, increased breathing rate

Regional heterothermy

Countercurrent exchange

Evaporation: costly  loss of water: ultimate line of defense

Mammals and birds in hot environments
heat loss
Three active mechanisms:

Sweating: common in human  loss of water and salts in plasma, absent in some species such as rodents, rabbits

Panting: in birds, some mammals such as dogs

Gular fluttering in birds

Consequences: Animals adapt to changing temperatures, especially winter/summer acclimatization

Evolutionary changes:

Heat loss
hibernation estivation daily torpor
A mean to escape the demands of homeothermy


Controlled hypothermia

Body temperature fall to close approximate ambient temperatures

During winter  hibernation

During summer  estivation

During certain part of the day  daily torpor

Hibernation – Estivation – Daily torpor
Most likely the animal turn down its metabolism  cooling

Animals control their arousal

Animals arouse from hypothermia once in a while during the hibernation

Animals able to thermoregulate if the temperatures fall to levels too low

Animals need to prepare for hibernation by storing fat

Several mammal groups use hibernation to survive winter

Rare in birds

controlled hypothermia
Some species allow their temperature to decrease but not to ambient temperature

Chickadee’s temperature decrease by 7oC

Bears temperatures reach31-33oC

What are the advantages of such process?

Compared to no hypothermia

Compared to full hypothermia

Controlled hypothermia
warm bodied fishes
Most fishes are poilokilotherm. However, larger predator fishes such as some sharks and tunas have muscles which have a higher temperature than the body

They need to swim vigorously in order to catch fast preys

They have:

A higher metabolic rate in these muscles  heat production

However, in order not to loose it through blood circulation  presence of a counter-current mechanism.

Warm-bodied fishes
endothermy in insects
At rest, not enough heat is produced to warm up the insect

Heat is produced by muscles during flight

Temporal and spatial heterothermy:

Endothermy when active only and in the thorax muscles

Ex: sphinx moth, bumble bee (the flight muscles can be used for shivering)

Endothermy in Insects
endothermy in insects28
The higher the temperature, the more efficient the flying  the more energy and heat produced

They thermoregulate by controlling blood circulation from thorax to abdomen, by varying the degree of body insulation and by controlling muscle activity

Ex: Bumble bee warm themselves before being able to fly (sun exposure and shivering). Then, flight can maintain the warmth

What’s a mosquito to do in order to fly?

It has a large body surface and very low weight (muscles).

It cannot produce much heat and loose it fast

Endothermy in insects