Transcript Migration Physiology Guest Lecturer: Eddy Price

Migration Physiology
Guest Lecturer: Eddy Price
•
What is migration?
Best described as a
syndrome of traits:
1. Persistent prolonged
movement
2. Straightened course of
movement
3. Undistracted by usual
stimuli (e.g. food,
mates)
4. Distinct departure and
arrival behavior
5. Reallocation of energy
in advance of migration
What is Migration Physiology?
• Migration is a complex syndrome of traits;
involves many physiological changes.
• Exercise physiology
– Migratory Birds:
– Metabolic rates twice those achievable by mammals
of similar size high intensity exercise!
– Up to 11 days without stopping to rest!!
– Migrants are extreme endurance athletes
• Also: Endocrine system, biological clocks,
navigation mechanisms, specialized structures
3 Metabolic Fuels
• Carbohydrate (mostly
glucose) is stored as
glycogen in liver and
muscle.
• Protein has no storage
form. It is all functional
(enzymes, transporters,
structural).
• Fat is stored as
triacylglycerol in adipose
and muscle.
• There are limitations to
storing fuels in muscle
Exercise Physiology
• Movement of oxygen
and substrate to the
muscle mitochondria.
• Mammals also use
substantial
INTRACELLULAR
glycogen (and lipid)
stores
Which fuel is used during exercise?
• Carbohydrates, Protein, or Fat?
Carbohydrate Oxidation
Oxidation (% VO2max)
Fat Oxidation
Exercise Intensity
(%VO2 max)
Exercise in mammals
• “Carbo loading” by human endurance
athletes fills intramuscular and liver
glycogen stores
• “Hitting the wall” occurs when glycogen
stores are exhausted. Only fat is left, and
only LOW intensity exercise is possible.
Mechanical Power
Birds can’t afford to “hit the wall”
Flight Speed
Which fuel is used during exercise?
• Carbohydrates, Protein, or Fat?
Carbohydrate Oxidation
Oxidation (% VO2max)
Fat Oxidation
Birds are
different!!
Exercise Intensity
(%VO2 max)
Migrants primarily use fats!
• So, why do migrants use fat?
Glycogen
(carbohydrate)
Protein
Lipid
17.5
17.8
39.6
Water content
(%)
75
70
5
Energy Content
WET matter
(kJ/g)
4.4
5.3
37.6
Energy Content
DRY matter
(kJ/g)
Fat is ~9 times more energy dense than other
substrates!!
More fuel considerations
• Why use protein or glycogen at all?
– Salmon use up non-essential organs:
• Early in migration: use mostly fat
• Later in migration: fat is depleted, use protein from
catabolizing gut, then white muscle. Protect red
muscle and heart.
– Birds may tailor their muscle size to their
mass, which changes as they fly
More fuel considerations
• Using protein or glycogen
can also:
– Liberate water
– Replenish Krebs Cycle
intermediates (Fats burn in the
flame of carbohydrates)
– Fuel anaerobic exercise
• Inclement weather
• Burst performance (fish jumping
falls)
Water content (%)
Glycogen
(carbohydrate)
Protein
Lipid
75
70
5
Making use of fat
• In order to use lots of fat, a migrant needs
to:
– Store lots of fat!
– Increase fat transporters
Gaining Weight
• Generally, longer distance migrants have
higher % body fat.
• Monarchs can carry 60% of body mass as
fat, Aphids only about 30%.
Gaining Weight
• Generally, longer distance migrants have
higher % body fat.
• Monarchs can carry 60% of body mass as
fat, Aphids only about 30%.
• Birds up to 50% body mass)
• Behavior changes, predation risk
Guts Don’t Fly
• Digestive organs important for gaining
weight.
• But, they are not important in locomotion
Mass of digestive
organs
Day
Arrive at stopover
Leave Stopover Site
Mixing Fat and Water
• Moving fat through the body is difficult!
• Requires transporters (Fatty Acid Binding
Protein, Fatty Acid Translocase)
Muscle Cell
Fatty
Acids
FAT
FABP
Mitochondria
• Locusts can develop into
a migratory form when
conditions are right
•Locusts must increase FABP in order to
migrate.
•FABP becomes nearly 20% of all
protein in the muscle!!!
Migration
•Western Sandpipers migrate from Canada to Panama
•Also require increases in FABP
FABP is LOW in winter
and before migration
FABP is High
during migration
Other aspects of exercise
physiology
• Locomotory muscle
mass increases
• Mitochondrial density
increases
• Capillary density
increases.
• Increased Hematocrit
More migration physiology
• Biological Clocks
– Circadian rhythms:
• Birds generally migrate at night, must coordinate
daily pattern of feeding and catabolism (feeding
time vs. departure time).
– Circannual rhythms:
• Most animals migrate at particular times of the
year.
Seasonality
• Seasonality – behavior and physiology
vary over the year.
– Reproduction, migration, hibernation, fat
cycles, molt.
– Photoperiod is a major cue
• Absolute Day Length (predominant cue)
• Changing Day Length
Seasonality
• Invertebrates
– May enter diapause, cease reproduction, and
migrate. Insects at high latitudes may
diapause at longer day lengths
• Vertebrates
– Photorefractoriness:
• Animals become insensitive to an absolute day
length that has an effect at a different time.
• Has to be reset by short days
Circannual Rhythms
• Circannual Rhythms are free-running
without environmental cues.
• Stronger in species that have unreliable
cues or where seasonal timing is very
important
– Long-distance migrants
– Underground hibernators
More migration physiology
• Endocrine system
– Coordination of behavior and physiology
– Examples:
• Insects: Juvenile Hormone can stimulate flight at
intermediate levels, but suppress migration at high
levels
• Fish: Thyroid Hormone (T4) increases swimming
activity and lipid mobilization. Cortisol stimulates
lipid metabolism and stimulates salt water tolerance
• Birds: Thyroid Hormone increases fattening and
restlessness. Corticosterone is major metabolic
regulator.