Migration Physiology

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Migration Physiology

• Guest Lecturer Eddy Price

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What is migration?

• Best described as a syndrome of traits
• Persistent prolonged movement
• Straightened course of movement
• Undistracted by usual stimuli (e.g. food, mates)
• Distinct departure and arrival behavior
• Reallocation of energy in advance of migration

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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

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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

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• Exercise Physiology
• Movement of oxygen and substrate to the muscle
  mitochondria.
• Mammals also use substantial INTRACELLULAR
  glycogen (and lipid) stores

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Which fuel is used during exercise?

• Carbohydrates, Protein, or Fat?

Fat Oxidation
Carbohydrate Oxidation
Oxidation ( VO2max)
Exercise Intensity (VO2 max)
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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.

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Birds cant afford to hit the wall
Mechanical Power
Flight Speed
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Which fuel is used during exercise?

• Carbohydrates, Protein, or Fat?

Fat Oxidation
Carbohydrate Oxidation
Oxidation ( VO2max)
Birds are different!!
Exercise Intensity (VO2 max)
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Migrants primarily use fats!

• So, why do migrants use fat?

Fat is 9 times more energy dense than other
substrates!!
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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

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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)

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Making use of fat

• In order to use lots of fat, a migrant needs to
• Store lots of fat!
• Increase fat transporters

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Gaining Weight

• Generally, longer distance migrants have higher
  body fat.
• Monarchs can carry 60 of body mass as fat,
  Aphids only about 30.

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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

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Guts Dont Fly

• Digestive organs important for gaining weight.
• But, they are not important in locomotion

Mass of digestive organs
Day
Leave Stopover Site
Arrive at stopover
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Mixing Fat and Water

• Moving fat through the body is difficult!
• Requires transporters (Fatty Acid Binding
  Protein, Fatty Acid Translocase)

Muscle Cell
Fatty Acids
FABP
FAT
Mitochondria
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• Locusts can develop into a migratory form when
  conditions are right

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• Locusts must increase FABP in order to migrate.
• FABP becomes nearly 20 of all protein in the
  muscle!!!

Migration
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• Western Sandpipers migrate from Canada to Panama
• Also require increases in FABP

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FABP is LOW in winter and before migration
FABP is High during migration
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Other aspects of exercise physiology

• Locomotory muscle mass increases
• Mitochondrial density increases
• Capillary density increases.
• Increased Hematocrit

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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.

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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

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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

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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

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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.