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Hungry, Hungry Penguins
Long-term fasting and re-feeding mechanisms
by Jacqui Andrews, Matthew Peraica, Will
Mischler, Colleen Griffin and Bridget TeeKing
Penguins as a Model Organism
● Excellent for studying the interaction between body energy and fasting
○ Many bird species live through cycles of fasting and feeding
○
shows the limits of body fat depletion and the specific mechanisms of fat consumption
● Feeding and breeding
○ Feeding has to compete with other activities such as moulting, breeding and reproduction
○
Have to choose between protecting egg and feeding
○ Have to choose between using protein for feather
growth or to maintain essential function
Three Traits of Penguin Physiology
Energy storage and usage while fasting
How does a penguin collect and store fat?
What constitutes the fat?
What macromolecules does a penguin diet find most essential?
Limitations of fasting
The three phases
Re-feeding
What happens when fat stores run low?
Energy Storage and Use While Fasting
What to store
Protein and body fat
How to save energy
Various tactics such as huddling
Fasting with a full stomach
Need to feed baby chick
What to Store
Storing body fat in adipose tissue
Can intake 1% of body weight daily during feeding
Storing body protein
Can only deplete to 50% total loss
Need protein for making new feathers
How much to store
Not too much- extended time feeding and
carrying too large reserves not favorable
Not too little- it needs to last period of egg
incubation
How to Save
● Lower loss to a minimum
● Saving energy
○ Lower metabolism
○ Low locomotor activity
○ Good thermal insulation in Kings
○ Huddling in Emperors
● Spare body protein
○ Adaptation to long term fasting
Fasting With a Full Stomach
● One parent will stay fasting for extended periods
of time to care for young; other parent forages
the ocean
● Incubate food in stomach for up to 20 days if
needed to feed new-hatched chick
○ Unsure how digestion is blocked
○ Up to 50% of fatty acids kept as free fatty acids
● Stomach pH maintained acidic
● Metabolism of food lipids by bacteria also
possible
Phases of Fasting
● Identifiable by the the specific daily body mass loss changes
Three Phases of Fasting
Phase I: adjustment, mobilization of fat stores to maximum, lower protein
utilization, daily body mass loss decreases, not really a thing in natural fasts,
begins in water
Phase II: economy, low and steady specific daily body mass loss, steady energy
expenditure with contributions by lipid and protein, most of time ashore
Phase III: increase daily body mass loss due to increase in protein catabolism
when fat stores reach low threshold
Phase II vs. Phase III
● The energy and protein
saving that occurs during
phase II will only work if
the penguin has a lower
amount of fat stored.
● At start of Phase III,
changes in protein
catabolism is immediate;
changes in fat catabolism
seen later
What Really Happens in Phase III?
● Progressive increase in specific and daily loss of body mass
○
More locomotor activity
● Increase protein usage to make up for lack of lipids left
○
Reflects increase in circulating plasma uric acid and urea, increase in
amino acid amount, and decrease in plasma protein
○
Result - decrease in lipid plasma
● Phase can be reversed with decrease in motor activity
Re-feeding Signal Hypothesis
At a given level of energy reserve
depletion, an endogenous “re-feeding”
signal stimulates the drive to re-feed
Mechanism
Response:
Spontaneous egg abandon
behavioral changes
Effectivity
Mechanism of the Re-feeding Signal
High levels of plasma uric acid, free fatty acids, and plasma corticosterone
and reduction in prolactin at critical body mass indicates phase III
metabolic status
Re-feeding triggered by the metabolic adjustments to these Phase III
characteristics
This has been supported by the metabolic signals that indicate the need to
re-feed in other animals
Response
Spontaneous egg abandon
Relief by partner usually occurs at 20-30% of
initial fat stores during phase II
Transitory abandon that progressively
increased to definitive abandon
Transition from lethargy to spontaneous
locomotion below critical body mass
threshold
energy-saving behavior abandoned in favor of
food-searching
Efficiency Of the Re-feeding Signal
Validity of the re-feeding signal to allow
penguin to survive fasting
Robin, et al. study: 100% of abandoning
penguins returned
Both abandoning and relieved birds
spent the same time re-feeding and
returned with the same body mass
Review: Diet of a Penguin
1. Storing and Using Energy while Fasting - Not too much, not too little, Low
energy usage
2. Fasting - Three Phases, Protein catabolism, increase in movement
3. Re-feeding - Chemical signal to eat and egg abandonment
Takeaway: Ways to Conserve Energy
Penguins use both protein and adipose tissue to store energy
Save energy
lower metabolism, little movement
Maintain body heat (natural insulation/huddling)
Incubate food to feed newborns
Takeaway: Phases of Fasting
Phase I
Occurs right away, fats catabolized, proteins conserved
Phase II
Steady low Body mass loss, lipids and proteins utilized
Phase III
More body mass lost due to increase in protein catabolism
Takeaway: Re-feeding
When energy reserves are low, metabolic signals trigger re-feeding
Abandons energy-saving mechanisms ignored in favor of food
Some would abandon eggs in order to re-feed but always return with higher
body mass
Final Thoughts
Refeeding signals in Penguins is effective in allowing penguins to survive
long-term fasting
This allows a Penguin populations to be stable while providing them with a
mechanism to “decide” between feeding, breeding, moulting and other
responsibilities
Penguins are great model organism for
understanding long term control of
energy storage and feeding