Biological Orientation ResponsesTropisms (plants only) – growth towards or away from a stimulus coming from one direction.

towards = positive, away = negative towards light positive phototropism, away negative phototropism

Taxes (animals and a few mobile plants) – movement of the whole organism towards or away from a stimulus coming from one direction. May be positive or negative. towards light – positive phototaxis, away – negative phototaxis

Kinesis (animals only) – non-directional response to a stimulus or a change in activity rate in response to a change in the intensity of the stimulus.

•Tropotaxis – 2 or more receptors which can simultaneously judge the intensity of the stimulus, the animal can find a balance between them. This allows the animal to move directly towards or away from the stimulus

•Klinotaxis – animal has only one receptor and needs to keep turning its head from side to side. In response to an increase in the stimulus intensity the animal increases its rate of head turning. Although he animal has no directional receptors, it can perform a directional response.

•Orthokinesis – a relationship between the speed of the reaction and the intensity of the stimulus.

•Klinokinesis – the rate of the turning and change of direction alter in relation to the intensity of the stimulus.

Nastic movements (plants) – this is a response to a stimulus which is independent of the direction of the stimulus, e.g. the opening and closing of flowers in response to changes in light intensity.

Homing (animals) – ability to find and return to home site.

Migration (animals) - annual mass movement of animals, from breeding areas to other non-breeding areas and then returning.

Homing

•Animals have to leave the home site to find food and mates but have to return again.

•Homing is the ability of an individual to return to the home site after being displaced.

•Home site could be a hive, nest, mound, burrow.

•Navigation is involved but generally homing relies on recognition of familiar landmarks

Migration•Regular, annual, or seasonal mass movements from a breeding ground to an area where they do not breed.

•Second site has food, water and optimal weather conditions.

•Migration is a response to environmental change, a genetic drive that is innate, or the animal has matured and has the need to reproduce

•True migration initiated by an internal clock or timekeeper in response to environmental cues

e.g. change in temperature, decrease in day length triggering zugunruhe

(migratory restlessness)

Migration

Advantages – remain in favourable conditions, grow larger, leave more young, constant food supply, reduces predation/parasitism/disease, greater genetic mixing, better breeding conditions, may lead to colonisation of new areas

Disadvantages – may get eaten by predators, caught in storms, starve, use up too much energy during the migration, huge energy investment

•Migration would not occur unless it had some reproductive or survival advantage.

•Migratory behaviour is inherited and maintained by natural selection.

Types of Migration

Dispersal – one way migrationOne way movement. Animal does not return to its original home range. Used to escape deteriorating habitats and to colonise new ones.

e.g. muskrat, locusts,

Original home range Breeding site

Breeding site

Breeding siteBreeding site

Breeding site

Return Migration •Animals move to a winter feeding ground •The same animals return to their home range in the spring which is where they have their breeding sites.• Return journey may not be the same path taken to the overwintering site.

•E.g. caribou, cuckoo, shearwater, turtles, whales

Dry season or winter siteBreeding site

Nomadic migration •One way movement away from the original home site. •Similar to dispersal but individuals may breed at several locations during their lifetimes.•No set pattern to the movement (directionless) •Each stopover is a potential breeding site•May also include temporary non-breeding stopovers for a dry or winter season

e.g. humans : Bedouin, Inuit

Non –breeding site

Breeding site

Breeding site

Remigration circuits •The return leg of a migration may have stopovers and may be completed by one or more subsequent generations. •Winter and dry season areas as well as stops at feeding areas by juveniles and adults•May include closed circuits where animals die after breeding

•E.g. salmon, monarch butterfly, eel

Second generation

First generation

Feeding stopover

Dry season/winter site

ORIENTATION FOR HOMING AND MIGRATION

Three types of orientation:• piloting• compass orientation• true navigation

Piloting • Movement from a familiar landmark to another until an

animal• reaches its destination.• Used over short distances using visual cues.

Compass orientation• Animal can detect a compass direction and travel in a

straight line• path until it reaches its destination.• Accomplished using magnetic field lines, chemical cues,

sound

True navigation• Determining one’s position relative to other locations.• Requires a map sense and a sense of timing

True Navigation•The ability to orient towards a target area without the use of landmarks and regardless of its direction

•Map sense – ability to be aware of the latitude and longitude of an area.

•Sense of timing – an internal clock that can compensate for the movement of the sun or stars.

•Both are required for solar and stellar navigation.

Methods used for NavigationVisual cues – animal learns its surroundings. Memorise the shape of coastlines, other topography of the area e.g. trees, streams, hills

e.g. digger wasps

Solar Navigation

•Requires a precise internal clock

•Use of the sun to navigate home/migrate. Sun always moves East to west.

•Some animals can detect polarised (due to differential absorption, some of the light becomes polarized plane of polarization tells position of sun)

•Enables them to detect where the sun is even with the smallest patch of blue sky.

e.g. honeybees – keep the sun on one ommatidium of their compound eye during the outward journey and on a corresponding opposite ommatidium on the return journey.

Bee indicates where a food source is to the hive, by doing one of two dances.

Round dance – points directly to a food source within 50m

Waggle dance – bee traces a figure 8. The axis of the waggle (in regards to the vertical nature of the comb in the hive) indicates the direction of the food in relation to the direction of the sun.The number of waggles indicates the distance. Fewer, slower waggles the further away the food is.

Birds – fly mainly during the day•Compensate for the changing direction of the sun related to time of day.

e.g. northern hemisphere bird flying south in autumn

9am flies 45º left of the sun3pm flies 45º right of the sun

•Retard internal clock with artificial light-dark cycles and the bird will fly in direction based on perceived time. Reset internal clock.

e.g. retard by 6 hours; bird released at 3pm sees sun at 9am and will fly west.

Star Compass

•Star compass orientation similar to sun compass.

•Groups and geometric patterns of stars are important.

•Generally based on the brightest (northern stars) stars as they move the least during the night.

•Rotational axis of star field (around North and South celestial poles) is important

•Requires precise internal clock

Magnetic Fields

•Animal has a magnetic compass

•Able to follow the magnetic field lines of the earth

•Direction and position derived from direction and inclination of field components

•Some animals have small amounts of magnetite in their brains these respond to magnetic fields and information is transferred to nerve endings and processed by brain

•Used by pigeons, whales, dolphins, turtles, salamanders, some bacteria, some bees

•Magnetic storms, over magnetic anomalies and orientation in room with manipulated magnetic field animals navigation disrupted

Homing Pigeon’s Orientation

•Pigeons can navigate hundreds of km to a goal, even with no visual cues to the path home.

•Appears that they have multiple cues

How do we know that?

When birds have clocks shifted by 6 hours (using artificial lighting), direction is off by 90 deg.

When sky is overcast (sun not visible), clock- shifted birds head off in correct direction. Appear to be using another mechanism independent of sun and time of day.

When birds are wearing magnets, they are confused on overcast days, but not on sunny days.

Chemical Navigation

Animals recognise and memorise chemical trails/markers to aid navigation

e.g. dogs, ants, salmon, eels

Ambient Pressure

Sensitivity to atmospheric changes – altimetere.g. pigeons

SoundInfrasound-frequency less than 10Hz. Travels long distancesHumans can not hear this low. Elephants communicate up to 8km using infrasound.

Pigeons may use sound of surf on beaches to aid navigation

Humpback whales – use sonar, ultrasound, infrasound

Bats – use sonar, ultrasound

Many animals use more than one method of navigation.

Many of the mechanisms used for homing and migration are

not yet fully understood.