Biology 272a: Comparative Animal Physiology

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Biology 272a Comparative Animal Physiology

• Animal Navigation

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Why do animals navigate?

• Reproduction
• Food and other resources
• Avoiding inclement conditions
• Finding home
• An ultimate question

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How do animals navigate?

• A proximate question

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Navigational Strategies

• Trail following/route learning
• Piloting
• Path integration
• Compass navigation
• Map-and compass navigation

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Trail following/route learning

• Trails may be visual (e.g. deer trails)
• Olfactory (e.g. pheromone trails in ants)

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Piloting

• Using landmark cues to find a known location

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Niko Tinbergen (1907-1988)

• Nobel prize for Physiology or Medicine (1973)
• PhD Thesis (32 pages long!) on navigation in
  digger wasps (Beewolves)

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Philanthus - Beewolves
Hymenoptera Crabronidae
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Piloting

• Homing pigeons (once in home area)
• Clarks Nutcrackers (food caching)

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Path integration

• Dead Reckoning
• Know direction Distance and calculate position
  from there
• Long way out, short way home

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Path integration in desert ants (Cataglyphis
fortis)
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How do ants know how far theyve gone?
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How do they know which direction theyve gone?

• Compass based on visual cues
• Celestial
• Sun position
• Polarised light

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Star compasses
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Star compasses

• Nocturnal migrating/flying birds
• Seabirds
• (some) migrating song birds
• Experiments
• Raise birds so they can see night sky, but not
  landmarks
• Raise birds in planetariums with weird star
  configurations

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Sun Compasses

• Need to know time of day
• If manipulate this, animal moves in wrong
  direction

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Sun Compasses
Fig 17.5
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Polarised light
The direction from which this polarised light
comes indicates the direction of the sun
Fig. 17.6a
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Polarised light
Fig. 17.6b
Polarised light means you can tell where the sun
is even on a cloudy day!
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How do insects see polarised light?
Ommatidium
Dorsal rim of Compound eye has particular focus
on polarised light
Aligned Rhodopsin molecules
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Magnetic fields theyre out there!
Fig 17.8
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Magnetic fields organisms can detect them!

• Magnetic bacteria use magnetosomes to orient to
  magnetic fields

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Animals can detect magnetic fields
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Migrating fin whales avoid areas of strong
magnetic fields
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How do we show that animals can actually detect
magnetic fields, and how do they do it?
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How do animals detect magnetism? I Trout

• Magnetite crystals associated with specialised
  cells in nose of trout
• If blocked, magnetic sense disappears

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How do animals detect magnetism? II - Birds

• Evidence that the nose is required for
  magnetoreception in pigeons
• cf. magnetite in trout nose
• Previous studies that blocked nose may have been
  blocking magnetoreception, not smell
• Most evidence suggests that magnetoreception
  map rather than compass in birds

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How do animals detect magnetism? III Birds (again)

• Resonant molecules?
• Some evidence from birds that light-affected
  molecules (e.g. rhodopsin) might return to
  unexcited state at different rates under
  different magnetic conditions
• Some magnetoreception is light-dependent

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How do animals detect magnetism? IIIa Flies

• A blue-light receptor is necessary for
  magnetoreception
• Gene identified, knockout flies dont respond to
  magnetic fields

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How do animals detect magnetism? IV Sharks

• Are known to swim in straight lines across long
  distances of open ocean
• Can detect electricity
• Ampullae of Lorenzini
• Is electromagnetic induction as they swim
  generating currents they can detect?

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Magnetic sense can provide animals with both a
map and a compass

• Magnetic anomalies

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Map and compass

• Many animals have a visual (or olfactory) map of
  their surroundings, which they combine with a
  compass to allow them to navigate.

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Fig 17.10
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Navigational Strategies

• Trail following/route learning
• Piloting
• Path integration
• Compass navigation
• Map-and compass navigation

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Reading for Tuesday

• Biological clocks
• Pp 383-389