Energy, Metabolism, & Fuel

Energy Metabolism

The sum of processes by which animals

acquire energy, channel energy into useful

functions, and dissipate energy from their

bodies.

Energy

Energy = the ability to do work

The transfer of energy defines

inanimate animate

Energy

4 Main Types:

◦ Chemical Energy

◦ Electrical Energy

◦ Mechanical Energy

◦ Heat

Physiological Work

All forms of energy are not equally capable of doing physiological work in animals.

Animals CANNOT use heat to do any form of physiological work

Physiological work: any process carried out by an animal that increases order. Ex:

◦ Synthesis of macromolecules such as proteins

◦ Generates electrical or chemical gradients

◦ Contracts muscles to move materials

Two Forms of Energy

High-grade Energy-

◦ can do physiological work =

chemical, electrical, & mechanical

Low-grade Energy-

◦ cannot do physiological work = heat

To Degrade Energy = transforming energy

from a high-grade form to low-grade. (heat)

Max Kliber

Kliber coined the term: “Fire of Life”

Life is a combustion process.

Explained relationship between oxygen,

heat production, and metabolism:

If you have an active life, and are using

oxygen, you are producing heat.

“Fire of Life”

OXYGEN

HEAT

METABOLISM

Antoine Lavosier

Lavosier:

Theory of Combustion and Metabolism

Lavosier’s equation:

Animal + Oxygen CO2 + H2O

Heat

Theory of Combustion and Metabolism

OXYGEN

HEAT

METABOLISM CO2

WATER

Fundamentals You are CONSUMING oxygen:

◦ Eat 1.4 lbs food/day

◦ Consume 1.5 lbs oxygen/day

You consume oxygen and food in order to produce ENERGY

Animals use energy for 3 major functions:

◦ Biosynthesis

◦ Maintenance

◦ Generation of external work.

3 Major Energy Functions

Biosynthesis:

An animal synthesizing its body’s constituents , such as proteins and lipids

Maintenance:

All the processes that maintain the integrity of the body.

Generation of External Work:

When an animal applies a mechanical force to objects outside its body.

Metabolism

Metabolism = Sum of all of the

biochemical processes occurring within the

cells and tissues of an organism.

Metabolic Rate = rate at which an animal

converts chemical energy into heat and

external work. Defined as: Metabolism

Time

Linking Metabolism & Fuel

The amount of ENERGY and HEAT

produced depends on the substrate eaten

Biological macromolecules found in food:

◦ Lipids (fats) = 9.3 kcal/gram

◦ Protein = 4.1 kcal/gram

◦ Carbohydrates = 4.1 kcal/gram

Importance of Metabolic Rate

Determinant of how much food an animal

needs.

Provides a quantitative measure of the total

activity of all physiological processes.

And can measure the drain the animal places on

the physiologically useful energy supplies of its

ecosystem.

Measuring Metabolism

Direct Calorimetry

Indirect Calorimetry

Direct Calorimetry

Directly measuring heat production

resulting from animal’s metabolism.

Rate of heat production = rate of heat

loss to the environment

Lavoisier’s

Direct

Calorimeter

Measure how

much heat is

produced by

measuring how

much ice melts.

1g ice melted =

334 J

Direct Calorimetry

Good measure because of the basic

relationship between these parameters:

Fuel + O2 Energy & Heat

Hard to do with many animals.

Indirect Calorimetry

Respirometry: measuring an animal’s rate of respiratory gas exchange with its environment. ◦ O2 Consumption

◦ CO2 Production

Material-Balance Method: measuring the chemical energy content of the organic matter that enters or leaves the animal’s body.

Other methods…

Respirometry

Closed Respirometry

Open Flow Respirometry

Both give discrete measures of metabolism

over relatively short time periods

Closed Respirometry

Difference between starting and ending [O2]

and [CO2] after a given amount of time

The mouse will

eventually become

hypoxic.

OXYGEN

ANALYZER

COMPUTER

VO2 PER MINUTE

Open-Flow Respirometry

VCO2 PER MINUTE

Open-Flow Respirometry

Can measure different

behaviors/ activity levels …

Mountain lions on treadmills!

Diving dolphins

Resting elephants

Can measure animals in air

or in water …

Linking Metabolism & Fuel

Each “fuel” demonstrates a characteristic

relationships between the amounts of:

(1) ATP produced

(2) O2 consumed

(3) CO2 produced

Linking Metabolism & Fuel

Respiratory Quotient = VCO2 / VO2

Carbohydrates = 1

Protein = 0.8

Fatty Acids = 0.7

RQ provides insight into which fuels are

being used to support metabolism.

Material Balance

Measure the chemical energy content of

all the food an animal eats over a period

of time, as well as, the chemical content of

the feces and urine eliminated over the

same time period.

Energy Ingested – Energy

Excreted = Metabolic Rate

Assimilation Efficiency

Other Methods

Fat Loss

Migrating Whales

Migrating Birds

Humpback Whales (no, this is not a

migratory bird, but

it is on a scale…)

Other Methods

Doubly-Labeled Water Technique

Isotopes D2 (dueterium) and 18O

◦ “heavy isotopes”

Administer dose of doubly-labeled water and measure elimination rates of D2 and 18O in the subject over time:

◦ regular sampling (blood draw) of heavy isotope concentrations in the body water.

Doubly Labeled Water

Time Between Sampling:

Small animals: as short as 24 hours

Larger animals: as long as 14 days.

Breakdown of isotopes (loss) allows us to calculate a long term metabolic rate.

Average daily metabolic rate is often also called the field metabolic rate (FMR).

Time-Energy Budgets

Categorize all of animals behaviors into a few categories

Using laboratory studies, or other means, determine metabolic rate of individual while engaging in those activities.

Using field observations, determine how much time individuals spend engaging in those activities during a 24 hour period.

Time-Energy Budgets

Multiply time spend engaging in a specific

behavior by the metabolic cost of that

behavior.

Sum energetic costs of all behaviors over

a 24 hour day to obtain total daily

energetic expenditure.

Sea Otter Activity Budget

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre MP MP Post MP Dept

Imm

Indp Imm ADULT

Perc

en

t o

f 24

Ho

ur

Day

Other

Swimming

Grooming

Foraging

Nursing

Resting

FMR of Southern Sea Otters

0

500

1000

1500

2000

2500

3000

3500

4000

Pre Molt

Pup

Molting

Pup

Post

Molt Pup

Dept.

Imm.

Indp.

Imm.

Adult

Daily E

nerg

eti

c E

xp

en

dit

ure

(kcal*

day-1

)

Other

Swimming

Grooming

Foraging

Nursing

Resting

Other Methods

Accelerometer Instrumentation

Records periods of rest and activity over a long period of time.

Very powerful can be used to estimate short term & long term metabolic rates.

Measures things such as limb-stroke frequency & body acceleration.

Accelerometer Instrumentation

Accelerometer Instrumentation

Allows the discrimination of behavioral

patterns while animals are out of sight.

Study showed gliding behavior improves

energetic efficiency in diving marine mammals:

◦ ie. Weddell seals realized a 9.2 to 59.6% reduction

in diving energetic costs.

Sink or Swim: Strategies for Cost-Efficient

Diving by Marine Mammals. Williams et al.

2000. Science vol. 288 p. 133-136.

Levels of Metabolism

Basal Metabolic Rate (BMR) /

Standard Metabolic Rate (SMR)

Resting Metabolic Rate (RMR)

Active Metabolic Rate VO2 Max

Levels of Metabolism

BMR is the minimum metabolic rate for an organism.

Measured under specific conditions.

Kliber Conditions =

◦ Fasted

◦ Adult

◦ Resting

◦ Thermally Neutral Environment

Thermal Neutral Zone

Environmental temperature (°C)

Meta

bolic

Rat

e

Lower critical

temperature

Upper critical

temperature

BMR

(Adapted from Eckert 2001)

Metabolic Regulation

Heat Production Active Heat

Dissipation

Tb

Levels of Metabolism

Factorial Aerobic Scope=

VO2 Max

BMR or SMR

Tells us something about the range of athletic capabilities an animal has.

◦ Average Mammal = 8-10

◦ Terrier Dog = 25

◦ MMs, Monitor Lizards, Lions = 5-7

Levels of Metabolism

BMR used for endotherms

SMR used for ectotherms b/c there is no thermally neutral zone for these animals

RMR is non-active, pre-exercise.

◦ Can be double BMR

Active metabolic rate is highly variable

◦ Can be10-25x BMR

Levels of Metabolism

Average daily metabolic rate

FMR = Field Metabolic Rate

◦ How much energy an animal is expending

over a 24 hour period

Or we may want to know how much

energy animals are expending in the wild

over an even greater period of time…

Energetic Budgets Energy in = Energy out

Energetic Demand =

◦ Activity Costs

◦ Maintenance Costs

◦ Thermoregulatory Costs

◦ SDA (cost of digestion)

Important to Remember: Metabolism varies with temperature, activity level, diet, lactation, pregnancy, time of day, age, gender, EVERYTHING.

Thermal Neutral Zone

Environmental temperature (°C)

Meta

bolic

Rat

e

Lower critical

temperature

Upper critical

temperature

BMR

(Adapted from Eckert 2001)

Metabolic Regulation

Heat Production Active Heat

Dissipation

Tb

4

9

14

19

24

0 5 10 15 20 25 30 35

Water temperature (oC)

Ox

yg

en

co

ns

um

pti

on

(m

LO

2k

g-1

min

-1)

(Williams et al., 2001)

4

9

14

19

24

0 5 10 15 20 25 30 35

Water temperature (oC)

Ox

yg

en

co

ns

um

pti

on

(m

LO

2k

g-1

min

-1)

(Adapted from Morrison et al., 1974; Costa and Kooyman 1984)

Surface Area to Volume Ratio

Specific Dynamic Action

Energetic Budgets

All of these things get factored into the

energetic budgets of these animals

However, we need to also think about

energetic budgets at different scales

Energetic Budgets

Species manage their energetic budgets

on very different time and spatial scales.

DAILY

SEASONALLY

Energetic Budgets

Individuals: Ein = Eout

Population: Ein > Eout