Chp 9Thermal 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

– 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)

• Can you give examples for each cases?

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

• 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

• 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

• Desert hare: Why such large ears?

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

• 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 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.

Effects of temperature at the biochemical levels

• Enzymes work faster at higher temperatures

• Lipids are more fluid at higher temperatures

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

• Why?

Thermoneutrality

• Varies with species– Some mouse species

have a TNZ of 30-35oC

– Eskimo dogs: - 25oC to 30oC

Thermoregulation

How does Fever relate to thermoregulation?

• http://physio1.utmem.edu/~blatteisc/index.php

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:– Fur– Posture– others

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

Insulation

• Pelage: pilomotor response

• Plumage: pilomotor response

• Blood flow: vasoconstriction/dilation

• Posture

Heat production

• Metabolism• Shivering• Non shivering

thermogenesis brown adipose tissue = brown fat

Mammals and birds in hot environments

• Behavorial defenses• Insulation• Body reactions such as

panting, increased breathing rate

• Regional heterothermy• Countercurrent exchange• Evaporation: costly

loss of water: ultimate line of defense

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:

Hibernation – Estivation – Daily torpor

• A mean to escape the demands of homeothermy– Torpor– Controlled hypothermia

• Body temperature fall to close approximate ambient temperatures

• During winter hibernation• During summer estivation• During certain part of the day

daily torpor

Hypothermia• 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

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.

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

• 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