Migration Physiology

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					Migration Physiology
Guest Lecturer: Eddy Price
           What is migration?
•   Best described as a
    syndrome of traits:
    1. Persistent prolonged
    2. Straightened course of
    3. Undistracted by usual
       stimuli (e.g. food,
    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
• Protein has no storage
  form. It is all functional
  (enzymes, transporters,
• 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
  glycogen (and lipid)
Which fuel is used during exercise?
• Carbohydrates, Protein, or Fat?
                          Fat Oxidation         Carbohydrate Oxidation
   Oxidation (% VO2max)

                                   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.
Birds can’t afford to “hit the wall”
Mechanical Power

                   Flight Speed
Which fuel is used during exercise?
• Carbohydrates, Protein, or Fat?
                          Fat Oxidation         Carbohydrate Oxidation
   Oxidation (% VO2max)

                                                                         Birds are

                                   Exercise Intensity
                                   (%VO2 max)
     Migrants primarily use fats!
• So, why do migrants use fat?
                    Glycogen      Protein   Lipid

Energy Content       17.5         17.8      39.6
DRY matter
Water content         75           70        5

Energy Content        4.4          5.3      37.6
WET matter

   Fat is ~9 times more energy dense than other
     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

                       Glycogen          Protein   Lipid
Water content (%)        75                70       5
           Making use of fat
• In order to use lots of fat, a migrant needs
  – 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
• But, they are not important in locomotion

Mass of digestive

                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)
Fatty          Muscle Cell


• Locusts can develop into
  a migratory form when
  conditions are right
•Locusts must increase FABP in order to
•FABP becomes nearly 20% of all           Migration
protein in the muscle!!!
•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
• Locomotory muscle
  mass increases
• Mitochondrial density
• Capillary density
• 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
• 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
• 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
  – 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
    • 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