Biology 272a: Comparative Animal Physiology

Biology 272a: Comparative Animal

Physiology

Animal Navigation

Why do animals navigate?ReproductionFood and other resourcesAvoiding inclement conditionsFinding ‘home’

An ultimate question

How do animals navigate?A proximate question

Navigational StrategiesTrail following/route learningPilotingPath integrationCompass navigationMap-and compass navigation

Trail following/route learningTrails may be visual

(e.g. deer trails)Olfactory (e.g.

pheromone trails in ants)

PilotingUsing landmark cues to find a

known location

Niko Tinbergen (1907-1988)Nobel prize for Physiology or

Medicine (1973)PhD Thesis (32 pages long!) on

navigation in digger wasps (‘Beewolves’)

Philanthus - Beewolves

Hymenoptera: Crabronidae

PilotingHoming pigeons (once in home

area)Clark’s Nutcrackers (food

caching)

Path integration“Dead

Reckoning” Know direction

& Distance and calculate position from there

Long way out, short way home

Path integration in desert ants (Cataglyphis fortis)

How do ants know how far they’ve gone?

How do they know which direction they’ve gone? ‘Compass’ based on visual cues

Celestial Sun position Polarised light

Star compasses

Star compassesNocturnal 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

Sun CompassesNeed to know time of day If manipulate this, animal moves

in wrong direction

Sun Compasses

Fig 17.5

Polarised light

The direction from which this polarised light comes indicates the direction of the sun

Fig. 17.6a

Polarised light

Polarised light means you can tell where the sun is even on a cloudy day!

Fig. 17.6b

How do insects see polarised light?

Ommatidium

Aligned Rhodopsin molecules

Dorsal rim of Compound eye has particular ‘focus’ on polarised light

Magnetic fields… they’re out there!

Fig 17.8

Magnetic fields: organisms can detect them!

Magnetic bacteria use ‘magnetosomes’ to orient to magnetic fields

Animals can detect magnetic fields…

Migrating fin whales avoid areas of strong magnetic fields

How do we show that animals can actually detect magnetic fields, and how do they do it?

How do animals detect magnetism? I TroutMagnetite crystals associated

with specialised cells in nose of trout If blocked, magnetic sense

disappears

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

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

How do animals detect magnetism? IIIa: FliesA blue-light receptor is

necessary for magnetoreception Gene identified, knockout flies

don’t respond to magnetic fields

How do animals detect magnetism? IV: SharksAre 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?

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

Magnetic anomalies

Map and compassMany animals have a visual (or

olfactory) map of their surroundings, which they combine with a compass to allow them to navigate.

Fig 17.10

Navigational StrategiesTrail following/route learningPilotingPath integrationCompass navigationMap-and compass navigation

Reading for TuesdayBiological clocksPp 383-389