Transcript 2672aLec22
Biology 272a: Comparative Animal Physiology Animal Navigation Why do animals navigate? Reproduction Food and other resources Avoiding inclement conditions Finding ‘home’ An ultimate question How do animals navigate? A proximate question Navigational Strategies Trail following/route learning Piloting Path integration Compass navigation Map-and compass navigation Trail following/route learning Trails may be visual (e.g. deer trails) Olfactory (e.g. pheromone trails in ants) Piloting Using 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 Piloting Homing 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 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 Sun Compasses Need 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 Fig. 17.6b Polarised light Polarised light means you can tell where the sun is even on a cloudy day! How do insects see polarised light? Ommatidium Dorsal rim of Compound eye has particular ‘focus’ on polarised light Aligned Rhodopsin molecules 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 Trout Magnetite 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 lightdependent How do animals detect magnetism? IIIa: Flies A blue-light receptor is necessary for magnetoreception Gene identified, knockout flies don’t respond to magnetic fields 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? Magnetic sense can provide animals with both a map and a compass Magnetic anomalies 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. Fig 17.10 Navigational Strategies Trail following/route learning Piloting Path integration Compass navigation Map-and compass navigation Reading for Tuesday Biological clocks Pp 383-389