Orientation, Navigation and Homing | Zoology Optional Notes for UPSC PDF Download

• Orientation is the position of the animal with reference to gravity or resource. This is the position the animal maintains in order to reach the resource. Positional orientation is to maintain upright posture against gravity for which vertebrate have membranous labyrinth and invertebrate statocyst.
• Object orientation takes place when the animal tries to approach an object which may be food or water. Aquatic animals move vertically in pond or lake which is called strato-orientation. When the animals try to move from grassland to forests, deserts or mountains it is called zonal orientation. Animals which migrate long distances generally possess topographical or geographical orientation.

Kinesis

Kinesis is the movement of an animal in response to stimuli. It may be oriented or undirected movement depending on the source of stimulus. The response may be proportional to the intensity of stimulus.

• Klinokinesis is the change of direction during movement which may increase or decrease in the light of intensity. Generally the animal moves right and left alternately to compare the direction of stimulus to gain correct orientation. Animals having single receptor show alternate movements. Caterpillar and maggots looking for the sites of pupation vacillate while moving.
• Orthokinesis depicts speed of locomotion which s related to the intensity of stimulus and accumulation of action specific energy in the animal. Whole body of the animal is involved. For example, burrowing animals such as Ammocoete larvae of lampreys burrows in sand away from light. Cockroaches move from brighter areas to darkness.

Different types of kineses are termed with respect to the stimulus, e.g. hygrokinsis is with respect to humidity as in isopods; photokinesis in which stimulus is gradient of light and chemokinesis is with respect to chemical stimuli.

Taxis

Taxis is the orientation of the animal with reference to the direction of stimulus in space. Movement can be towards or away from the stimulus and depending upon the stimulus it can be names as follows: hygrotaxis (humidity); geotaxis (gravity); chemotaxis (taste or odor); thermotaxis (temperature); anemotaxis (air current); rheotaxis (water current); phototaxis (light intensity); phonotaxis (sound waves); astrotaxis (sun, moon and stars); menotaxis (angle to the stimulus); mnemotaxis (based on memory).

• Klinotaxis occurs in those animals which have single receptor, as in Euglena, which compares the intensity of stimulus by alternate lateral movements. Similarly in the maggots of Diptera the light sensitive organ is a cluster of cells above and behind the mouth and the negative response to light is compared by flexing movement of body.
• Tropotaxis is found in animals which have paired receptors as eyes in Planaria. Animal gets equal inputs on both the receptors and hence it can move in straight line towards or away from light. If one eye of an insect is painted black it makes circling movements towards the side of painted eye.
• Telotaxis is found when animal has a choice between the positive and negative stimuli or when the animal does not have a balanced input on the two receptors. Orientation is effected by fixing the image on one side by moving the head and making a choice. Honey bee seeing two light sources flies to any one by making a choice.
• Menotaxis involves maintaining a constant angle in relation to the source of stimulus. Nocturnal moths have a habit of flying by keeping the light source (usually stars and moon) at right angle to the body so that they can fly parallel to the ground. But when they do the same with artificial light that is to closer, they are forced to fly in circles. Honey bees fly from their hives to the flowers by maintaining a constant angle to the sun as revealed by the wagging dace of the scout bees. The angle to the sun is remembered by foraging bees while watching the dance on the vertical surface of the comb. Foraging bees then fly towards the food source maintaining the same angle to the sun.
• Mnemotaxis was first described by Kuhn (1919). This is orientation based on memory that was studied by Niko Tinbergen (1951) with his experiment on digger wasp. Wasp circles around the nest and carries a memory map of the nest and its surroundings, which helps it to accurately orient itself and return to the nest. This is also called zonal orientation and geographical orientation which involves distance, direction and landmarks that make topography of the area and help the animal in homing to its nest.

Navigation & Homing

• Migratory animals which cover long distances either to reproduce or to escape from the harsh climate must find their way accurately over oceans, deserts, forest and mountains. Fishes, birds and many invertebrates possess extraordinary capabilities to cross oceans, deserts and mountains in order to reach their destination.
• Invertebrates such as crustaceans, amphipods, ants, bees and wasps possess strong homing and navigational instinct and are guided by the sun, moon, stars and topography of the area in following accurate route. Monarch butterflies migrate thousands of kilometers from Canada to Mexico to escape harsh winter and return back accurately to the same place.

Fish Navigation

• How fishes find their way in huge expanses of sea and reach their destinations which lie thousands of kilometers away has been a mystery. It is believed that they orient by the positions of stars and moon in the night sky and sun in daytime to find the direction of swimming.
• They also make use of temperature gradients and ocean currents which help them in swimming and also in navigation. However, it has been experimentally proven by A.S. Hasler that salmons are guided by the odour of their parent stream during return journey.
• Odour map gets imprinted in their brains when they migrate as larvae from tributaries to the sea and they can navigate back from the sea using this odour map when they become adults. Eels can also migrate to Sargasso Sea using similar odour maps but how their larvae, leptocephali find their way back to the river mouths, crossing vast stretches of Atlantic Sea is a mystery. Probably their parents leave some kind of odour trails during their journey.

Navigation In Birds

• Birds use a number of methods to find their way during migration. Many use celestial navigation, a method of orienting the body to the arc of the sun, to the phases of the moon, or to the pattern of stars in a particular season, which is called menotaxis. Hummingbirds and pigeons are able to determine the position of the sun even on overcast days because they can detect the ultraviolet radiation it emits.
• Experiments in planetarium on night migrant birds, such as white throated warblers and indigo buntings reveal that they orient themselves by the position of stars in the night sky.
• Some birds are sensitive to coriolis force that arises by deflection of winds in the northern hemisphere by earth’s rotation.
• Some diurnal birds use topographical landmarks such as mountains, river valleys, and forests to orient themselves on the migration route. Some are able to detect infrasound or low-frequency sounds that are produced by ocean waves. Many birds, particularly seabirds, identify their destinations by characteristic odours.
• Many birds possess instinct or some kind of internal compass or biological clock that guide them through the route of migration. Young birds follow the migration route accurately without previous training or experience by their inherent capacity to navigate.
• Some birds such as oil birds of South America and Himalayan cave swift possess echolocation and can be guided by it.
• The classic experiment proving the internal-clock theory was done by German Gustav Kramer during the early 1950’s. He placed Starlings wanting to migrate in a cage from which they could see the sun. The birds would sit looking in the direction toward which they wanted to fly. Significantly, if the Starlings couldn’t see the sun, they didn’t face in any particular direction.
• Also during the 1950’s, the German Franz and Eleonore Sauer did a similar experiment with birds that could and could not see the night stars and arrived at similar results. Certain species can orient themselves according to the sky’s major stars. In fact, an experiment with Mallard Ducks found that if the moon is so bright that important stars are hidden by glare, released ducks can’t orient themselves as well as on darker, moonless nights.
• Some birds, such as pigeons, are sensitive to changes in the earth’s magnetic field because of the presence of magnetite in their head and neck muscles. During early 1970’s, W.T. Keeton tied small, bar magnets on the backs of pigeons. When released at locations the birds had never seen before, the pigeons with non-magnetic bars found their ways home but those with bar magnets got confused.
• In a 2007 German scientists found tiny iron oxide crystals in the skin lining of the upper beak of pigeons, which might be of help to the birds to sense the earth’s magnetic field and assist them to identify their geographical position.
• The researchers also discovered cryptochromes, which change their chemistry in the presence of a magnetic field, in the retinas of migratory birds’ eyes. The molecules might then affect light-sensing cells in the retina to create images due to magnetic field and help the bird to navigate during flight.
• Infrasound travels much farther than ordinary sound and it comes from many different natural sources, including ocean waves, surf, winds, storms, earthquakes and other geologic events. It is believed that birds can hear infrasounds that we cannot hear and hence they possess this accessory navigational capability.