MIGRATION: Cause

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MIGRATION Cause Function

• WFSC 422 Ethology
• Presentation 3.2

Dr. Jane M. Packard, WFSC TAMU j-packard_at_tamu.edu
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monarch
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Migration Pattern of adaptation (e.g. snapshot)

• Structure (Cause)
• Sensory systems
• Motivational systems
• Neuromuscular systems (swim, fly, walk)
• Function
• Animal moves into climatic (physical) conditions
  within its tolerance range
• Those genotypes that migrated were more likely to
  survive/reproduce than those that did not

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Worldwide migrations
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Example Eels (European American)

• Cause- juvenile Alewives
• Carried by saltwater currents from Sargasso Sea
  to coast
• Follow freshwater gradient upstream at rivers
• Cause- mature adult eels
• Carried by river currents heavy rains to the
  ocean (lose tolerance to freshwater)
• Follow unknown stimuli to the Sargasso Sea

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Example Eels (continued)

• Function- juveniles
• Those that moved to coastal rivers found more
  food and grew to reproductive size
• Those that did not migrate never grew large
  enough to reproduce
• Function- mature adults
• Those that left rivers and spawned in Sargasso
  Sea had more offspring survive (few predators)
• Those that spawned in the rivers passed on few
  genotypes because all the predators ate the eggs

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Example Monarch butterfly migration

• CAUSE Spring/summer-
• fly north and reproduce
• Offspring fly north reproduce
• CAUSE Fall-
• dont reproduce and
• fly south to Mexican Volcanic mountain forest
  where they overwinter
• West of Rocky Moutains, they fly to San Juan
  Capistrano in California

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Example Monarchs (continued)

• FUNCTION Those that flew north in spring
• found more growing milkweeds,
• food for caterpillars when those plants dried up
  in the south
• FUNCTION Those that flew south and didnt
  reproduce in the fall,
• survived the cold dry winter in protected
  forests,
• reproduced early the next spring on slopes of the
  mountains

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SUMMARY

• Structure (Cause)- think in terms of genotypes
  that code for sensory, motivational action
  systems
• Function- those genotypes that avoided extremes
  were more likely to survive reproduce than
  those that did not
• Examples eels monarch butterflies

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Action Items

• Answer Q3.3 3.4
• Search for key authors Brower, L or Urquhart,
  FA
• Post to WebCT discussion Unit 3