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
       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?
                          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
                                                                         different!!


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

Energy Content       17.5         17.8      39.6
DRY matter
(kJ/g)
Water content         75           70        5
(%)

Energy Content        4.4          5.3      37.6
WET 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)

                       Glycogen          Protein   Lipid
                    (carbohydrate)
Water content (%)        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)
Fatty          Muscle Cell
Acids


                   FABP
        FAT

                          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           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
            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.

				
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