BioB34 Animal Physiology
Metabolic Rate: the rate at which animals convert chemical energy into heat energy. Different ways you can measure metabolism in animals:
1. Direct Calorimetry
- Measuring heat energy that animals are losing to the environment.
- Directly measuring animal’s metabolic rate
- It can be a bit of a hassle
2. Indirect Calorimetry
- Measure oxygen consumption and understand how that correlated with the amount of heat energy lost by the animal.
- Most common method used to measure the metabolic rate of the animal.
4. Doubly Labelled Water Technique
- Developed around 1950s
- Came into prominence in 2000 when Ken Nagy made tremendous # measurements of metabolic rate - How does it work? Don't forget about the age old question of What is the similarity between analogy and homology?
Most common water molecule found in the environment, in animals etc.
Makes up about 99.7% of all the water found on Earth.
Oxygen-16, 2 Hydrogen-1
• Synthesize or buy pre-synthesized doubly-labeled water in which the following water molecule is present.
Oxygen-18 (2 additional neutrons), making it a little heavier Don't forget about the age old question of Which type of research is used to describe characteristics in a population?
2 Hydrogen-2 (1 additional neutron each), making that heavier too
• Two isotopes that make it different from “regular” water.
• Inject this doubly-labeled water into an animal whose metabolic rate you want to measure • Wait about an hour or two for the doubly-labeled water to get distributed equally in the body of the animal
• Then take the blood sample of the animal
• From the blood sample, measure the concentration of the 2 heavy isotopes (H2 and O18) in the blood of the animal
• Now let the animal go into its environment to live its normal life
• Now capture the same injected animal a few days after and take a blood sample
• Measure the concentrations of the isotopes in the blood
• The concentrations would now be LOWER than at the time of the injection because now the isotopes have started to leave the body of the animal Don't forget about the age old question of What was the result of bargain/compromise of 1877?
• Hydrogen-2 would leave the body of the animal as a water molecule
• Using these measurements, calculate the rate at which the hydrogen-2 has left the body of the animal, you can also measure the rate of water loss
• Oxygen-18 has two ways of leaving the body of the animal
i. By the water molecule (H2O)
ii. By the carbon dioxide molecule (CO2)
• If you now calculate the rate at which the Oxygen-18 has left the animal’s body, you now have the measure of the rate of water loss and CO2 production.
• The difference between these values then would give us just the CO2 production rate • These measurements can now be used to calculate the animal’s metabolic rate because, as we know, there is a defined Don't forget about the age old question of What are some examples of credence goods?
Don't forget about the age old question of Which factors influence sexual arousal and response?
stoichiometric relationship between CO2 production and heat energy lost • Here, we are using an indirect measurement (CO2 production) rather than O2 consumption to estimate what is the actual heat energy lost by this animal
- This technique is used most commonly to measure Field Metabolic Rate (FMR). FMR is the metabolic rate of an animal while it is out in the field/ in its natural environment.
Another commonly measured metabolic rate is the Maximal (Aerobic/ Sustainable) Metabolic Rate (MMR).
MMR is the highest metabolic rate an animal can maintain over long periods of time. ** Sustainable = long term We also discuss several other topics like What characterizes terrestrial planets?
How to measure MMR?
Ex1: Rat running on treadmill.
Ex2: Swim Flume (fish treadmill)
- As the propeller turns, it pushes water
towards the fish.
- The fish, now to survive, swims against the
current of the water.
- To measure the fish’s metabolic rate, make
the propeller go faster and faster, at which point you
will now be able to depict the speed of the fish that
it can maintain.
- While doing so, the oxygen sensor measures
how much oxygen the fish is removing from water as it swims.
- How relevant is this measurement to the actual life of the fish?
- Study (Bonefish)
• 9 bonefish had been given an ID#.
• These bonefish were equipped with a device that could measure the metabolic rate of the bonefish when the fish was swimming in its natural habitat.
o The percentage of time each of these fish spent on a certain level of metabolism showed that every bonefish spent no or close to no-time at their maximum metabolic rate.
o Bonefish are living at about half of the maximal metabolic rate.
o Bonefish are at most 5% of the time at their maximal metabolic rate.
o This shows that the measurement of the MMR are not very relevant to the actual life of the bonefish.
- Study (Sockeye Salmon- SES)
• SES spend their adult life in the Pacific Ocean.
• When they are ready to reproduce, they travel from the Pacific Ocean to the Fraser river to the stream of the Fraser river they were born in.
• The male SES then dies after reaching their destination.
• Some final destinations are close to the river, some are very far.
• Here, timing is of the essence. Therefore, the SES all leave at the
same time (during the reproductive season) but due to varying
differences, the salmons that have to travel far, have to swim a lot
faster than the ones that have to go near.
• Therefore, the SES that must go long, have a much higher
maximal metabolic rate.
• The MMR is a very important part of their lives.
• Why? If they swim slow,
i. they will arrive to their breeding ground after someone else has occupied their breeding ground. They will not get their choice of breeding habitats.
ii. they will reach the breeding ground at a time NOT optimal for reproduction. The time when the maximum resource availability is starting to reduce.
The most common metabolic rate physiologists measure is called the Basal (Standard) Metabolic Rate (BMR).
BMR and Standard Metabolic Rate are distinctly different.
Basal Metabolic Rate (BMR)
- only applied to a group of animals that are endothermic (warm-blooded animals – mammals & birds)
- an animal’s metabolic rate under the following conditions:
i. in its thermo-neutral zone
➢ the range of ambient or environmental
temperatures over which the animal can maintain
a constant body temperature without using its
➢ no metabolic heat is being produced.
ii. at its typical body temperature
➢ animal must not be torpid
+ many animals and birds go through
a period of metabolic suppression
+ in hibernation, the animal’s metabolism and body temperature drop.
+ they should be at their typical body temperature
iii. post-absorptive and NOT post-prandial
➢ Post-prandial means recently fed.
➢ Post-absorptive means NOT fed recently.
➢ Animal should not be digesting or dealing with
the food it has consumed.
➢ After feeding, an animal’s metabolic rate
increases and stays high for long periods after
➢ Energy is being spent to fill up an animal’s
➢ Increase in metabolism that takes place post-prandial, is a phenomenon, called
Specific Dynamic Action (SDA). Another word used for this phenomenon is called Heat Increment of Feeding (HIF).
➢ Example: To measure the metabolic rate of a Tawny Owl, you have wait for at least 14-16 post-prandial, 10-12 hours would not be sufficient.
iv. Resting (but awake)
➢ Metabolism decreases by 3-10% when asleep, depending on the organism.
➢ Reproduction is energy-intensive.
➢ The metabolic rate, around the time of
giving birth (40-50 days before giving
birth - the metabolic rate is higher) and
between (10-30 days after giving birth- the
metabolic rate is tremendously high).
Why? Because at that time, the animal is
lactating. Lactation is one of the most
energy-intensive action in the life of a mammal.
➢ Stress elevates metabolic rate.
➢ The animal must be acclimated to the lab conditions (get used to the life in the
Standard Metabolic Rate (SMR)
- Applies only to ectothermic animals (cold-blooded animals – insects, fish & reptiles) - an animal’s metabolic rate under the following conditions:
- Why no thermoneutral zone and typical body temperature?
• Because ectothermic animals have varying body temperatures and they don’t regulate their body temperature metabolically.
v. * must report the temperature at which SMR was measured
- Metabolic rates are affected by temperature in these animals.
• The warner the animal, the faster the metabolism.
vi. * should be acclimated to that temperature
BMR and SMR gives us a good way to compare metabolism among species and/or individuals since the measurements are taken under the same conditions, be it in Canada or Africa.
However, it is questionable if all the conditions are being met because no one would necessarily know when the animal is unstressed, or when if was last fed, or if has been “knocked up” and is now reproductive etc.
If you are confident that all the conditions have been met, instead of calling the then measured metabolic rate BMR, you call it Resting Metabolic Rate – the animal can not be active.
BMR is a very relevant measure in the life of animals.
Study: BMR vs. FMR (Daily Energy Expenditure)
- The amount of energy animals use is very closely related to the measurement of their BMR. Therefore, upon the measurement of BMR, we can be assured that it nicely correlates with the actual daily energy used.
So … What is actually going on in the animal when we measure BMR? Why is the animal consuming energy or releasing heat when (according to the conditions to measure BMR) the animal only has to sit or stand and do nothing?
What are the actual origins of the Basal/ Standard Metabolic Rate? What requires energy in the animal at this point?
- Major processes that contribute to an animal’s metabolic rate
under these basal conditions.
i. Protein Synthesis (20-24%)
• 1000s of proteins are being made everyday that
have a half-life of between 30mins-2days.
• The proteins have to be rebuilt.
• Constant process of proteins getting worn out and damaged, degraded back to into amino
acid form and then building them back up into proteins is happening all the time. This takes a lot of energy.
ii. Na+-K+-ATPase (15-22%)
• In our blood (an extracellular fluid), we have a high
Proton Leak (18%)
concentration of sodium and a very low concentration of potassium ions and the reverse is true inside the cells (low [Na+] and high [K+]). These opposite concentrations have to be kept constant as much as possible.
PROBLEM: The cell membrane that separates the extracellular fluid from the cells is not a perfect permeability membrane. The cell membrane is leaky with these ions and therefore start to flow across the cell membrane, creating concentration gradients. This causes the concentrations of sodium and potassium to change. Therefore, the enzyme, Na+-K+-ATPase, has to counteract the flow – pump sodium out and potassium back in. This process requires energy.