Assignments relative to diving metabolism:

Diving in loons http://www.birdersworld.com/brw/amazingbirds/1995/9506_dive.html

Diving mammals review article http://www.biology.ucsc.edu/people/costa/PDFs/Costa1999PEUBS25.pdf

Do sec 1, 2 and 3a http://www.sfu.ca/bisc/bisc-305/jamie/tutorials/tutorial4/tutorial4.html  

Conduction, convection, etc definitions:   http://www.bartleby.com/64/C004/018.html

I. Definitions:

A. An ectotherm largely responds the same way classical chemical reactions respond.

B. An endotherm tries to control its body temperature by generating its own heat which will cause increased metabolism. Thus, the metabolic curve of an endotherm is highly related to the rates of heat loss and heat gain.

III. Effects of temperature on conventional chemical reactions.

A.

OR

ln(rate) = ln(constant) + (-EA /R) *(1/T)

Y = b + m * X

Thus a plot of ln(rate) vs. 1/T would yield a straight line where the

slope = -EA/R and the intercept = ln(constant).

(EA = activation energy) (R = gas constant = 2 cal*mole-1*°K--1 )

(Note that T is the absolute temperature °K)

Such a plot is called an Arrhenius plot

D.

Activation energy is a property of the given chemical reaction. The larger EA, the greater the effect the temperature has on the reaction. A value of EA = 0 implies that temperature has no effect on the reaction.

E. Q10 is the ratio of the rate of a reaction at one temperature divided by the rate of the same reaction at a temperature 10 C° less.

Q10 = rateT+10 /rateT

The larger the Q10 the greater the effect the temperature has on the reaction. A value of Q 10 = 1 implies temperature has no effect on the reaction.

F. Most chemical reactions fall in the range where:

EA = 10 to 25 Kcal/mole OR Q10 = 2 to 4

IV. Metabolism of an ectotherm

A. General:

B. Death occurs just below 0 °C because of water solidification (freezing). The most destruction occurs because of crystal formation which physically destroys the cells.

C. Death occurs just above 40 C because that is the temperature at which hydrogen bonds break thus leading to the denaturing of most proteins and enzymes.

D. Acclimatization - a change of animal chemistry to make it better suited for the environmental temperature. (Acclimatize technically means when an animal adjusts to a certain climate, acclimate involves adjustment to an artificially imposed environment)

Example for carp:

V. Ectotherm body temperature regulation. Ectotherms are often found to regulate their body temperature well by behavioral mechanisms.

A. Move to warmer or cooler areas (rocks, water, burrows, etc.)

B. Change coloration (darker colors absorb more heat)

C. Change surface area (larger surface area will lead to more heat exchange either in or out depending upon the differential of temperature between the animal and the environment)

D. evaporative cooling (e.g. panting)

VI. Endothermy

A. Regulation

1. 38-42 °C is the ideal and most efficient temperature for biological reactions. All endotherms regulate at these temperatures.

2. The mammalian "thermostat" is located in the hypothalmus of the brain - the 'master endocrine gland'.

3. Temperature sensors in the skin elicit behavioral temperature adaptations.

4. The largest amount of endotherm heat comes from the thoracic cavity and much of that heat is produced by the smooth muscles.

B. Conventional curve

Ta => ambient (environmental) temperature

Tb => body temperature

Tc => critical temperature (where metabolism starts to increase significantly because of excessive cold

C. How can an animal deal with excessive cold

1. Thermal conductance equation

a. :

where A is the surface area and Cr is the real conductance value.

b. Note that the equation is essentially identical to Fick's law of diffusion and essentially all of the same principles apply. (The major difference is that here we are talking about a heat flow instead of a chemical flow).

c. Note that Cr is the inverse of the insulation (I).

Cr = 1 / I

d. For endothermy it must be that heat loss equals heat produced which is proportional to metabolic rate. Therefore:

metabolic rate a A Cr (Ta -T b).

e. Note if the metabolic rate is plotted versus the ambient temperature that a straight line is described with a slope of -A*Cr and a metabolic rate intercept of Tb.

f. Note that at low temperatures the metabolic rate does increase linearly, that the slope does directly relate to the insulation, and the line does extrapolate through the body temperature.

2. Decreasing the surface area of blood exposure to the environment can obviously reduce the heat loss. This can be done behaviorally (drawing in all appendages, huddling, putting on clothing, seeking a warmer place, ...) and/or physiologically (reducing the blood flow to the skin surface and high surface area appendages).

a. Being big helps in preventing heat loss (less surface to volume ratio)

3. Insulation - fur, hair, blubber, feathers, insect scales, coats. These can sometimes be changed seasonally (or even instantaneously as in the case of a bird fluffing its feathers).

a. Note that the function of hair, fur, and feathers is not so much to increase the insulation, but rather it primarily functions to take advantage of the already excellent insulation value of air by preventing its movement thus preventing the loss of heat by convection. (All of these insulation methods are simply designed to immobilize air). The actual makeup of hair, etc. (keratin) would actually have a much higher conductance than air.

b. Blubber is often used as a insulator; it is about 10 worse than air but has obvious advantages for water animals.

4. Counter-current heat exchange can be used to prevent heat loss to extremities and is very commonly used. There are often alternate routes for the blood to help maintain the heat (counter current) or dissipate the heat (non-counter current).

5 Animals can increase their internal heat production by increased metabolism This is often through shivering- a rapid series of contractions of skeletal muscle.

6. Have darker skin or fur to increase the conversion of visible light into heat.

D. How can an endothermic animal deal with excessive heat?

1. Evaporative cooling. (This is about the only real way to cool when the ambient temperature is higher than the body temperature.)

a. Converting liquid water into gaseous water requires utilizes a substantial amount of heat:

580 cal/gram + H2O (liq) ----> H2O (gas)

b. Evaporative cooling can be achieved in several ways:

i. sweating

ii. panting

iii. licking

iv. urination onto the legs and then the urine evaporates.

c. All of these methods require metabolic work. This is one reason metabolism goes up at higher temperatures. (The other reason is that increased temperature causes faster chemical reactions)

d. Increased 'ventilation' (convection) can greatly help evaporative cooling. Panting has the advantage of a built in surface refreshing mechanism as air passes over the surfaces.

2. Reducing the insulation would help the animal release excessive body heat to the environment if the external temperature is in fact lower than the body temperature. If the external temperature is higher than the body temperature, then insulation would actually help prevent more heat from entering the body!! (e.g. the camel)

3. Increasing the surface area and increasing vascularization to the surface would help the animal release excessive body heat to the environment if the external temperature is in fact lower than the body temperature.

4. Reduce dark coloration.

5. Behavioral adaptation. (Burrowing, get in shade, get in water, etc.)

6. Store heat until a cooler time or place is reached at which point the heat can be released.

7. Selective cooling.

a. counter current exchange in the panting mouth and nasal regions can keep the brain a few degrees lower. (The brain is the organ most sensitive to excessive heat.)

VII. Unusual forms of heat production

A. Large swimming fish such as the tuna and shark keep their internal core several degrees higher than their environment. Their large size, high activity, and counter current heat exchange systems all help allow for this

B. Ontogenic endothermy

1. An animal at birth is frequently uninsulated as well as being small (thus a high surface area to volume ratio). Many such newborns behave ectothermically and depend upon their parents for temperature regulation. A larger eating rate is necessary for body growth and eventually for the metabolism necessary for endothermy.

2. Some newborn mammals have brown fat that is a tissue designed for high heat production.

C. Endothermic insects

1 One can maintain a body temperature of 35-40 °C during periods of activity, such as flying.

2. Insect flight muscle are metabolically the most active tissue known. Many insects cannot contract with sufficient speed, power, and frequency to keep the insect airborne unless they are at higher temperature. Such insects are covered by dense scales for insulation.

3. Preflight warm-up. In moths it often involves simultaneous contraction of opposing muscles giving the appearance of shivering.

4. Bees as a population can keep a hive at a high temperature compared to their environment. A queen bee can better maintain a higher temperature because of her larger size.

VIII. Topor - definition? Reduce metabolism, reduced body temperature, abandonment of homeothermy, dormancy.

A. Daily topor, hibernation, estivation. All occur when the cost of metabolism and homeothermy are too great compared to heterothermy.

B. The stresses that make the cost of metabolism too high are temperature extremes, food deprivation and water deprivation: a misbalance between energy supply and energy expenditure.

IX. Estivation - topor or dormancy over an extended period of time due to extreme heat. It can be costly to cool; and it gets more "costly" the less available is water.

X. Hibernation - topor over an extended period of time due to extreme cold. It is more costly to maintain body temperature the larger the difference between maintained body temperature and the ambient temperature. And it gets more "costly" the less food there is available.

A. Usually involves a great deal of preparation, both behavioral and physiological.

1. Food storage in hibernation chamber

2. Fat build up

3. Development of hibernation chamber

4. Fur or insulation build up

5. Undergo a series of deeper and deeper topor.

6. May involve an internal clock since animals kept in constant conditions may also hibernate.

B. Usually involves arousal in small vertebrates several times during the winter, at which time they arouse, eliminate wastes and may eat (at least every couple of weeks).

C. Hibernation, by classic definition, involves significantly lowered body temperature from the homeothermic value. Essentially become heterotherms.

1. Bears, by this definition, do not hibernate.

2. When the environmental temperature falls below zero, three types of phenomenon can be found in the animal kingdom, depending upon the species.

a. Die

b. Arouse to classic homeothermic body temperature.

c. Maintain a metabolism by a thermostatic set point to keep body temperature at 1-3 C°

3 Arousal

a. Body temperature usually increased by shivering and/or brown fat.

b. It can take from 15 min. to hours depending upon the size of the animal. For large (>750g) animals it tends to be impractical.

c. Energy savings - see daily topor.

D. Hormones seem to be greatly involved in both hibernation and arousal.

XI. Daily topor

A. Common in many small animals ( 50g). Bats and hummingbirds are two classics.

1. Small animals usually require high energy amounts of endothermy, yet such quantities may be only practically available during certain times of the day.

2. Small animals loose great deals of heat because of their large surface to body ratio and therefore differences between Tb and Ta can be significant.

B. Reduced body temperature

1. Energy savings. Mouse - enters topor at 15 C° and then immediate arousal - time 2.9 hrs. - cost 6.5 mlO2 /g. Compare to the cost of homeothermy was maintained for 2.9 hrs: 11.9 ml O2/g. A 55% savings! During the night the savings would be close to 90%.