Migration and navigation 1 Flashcards

1
Q

Why do animals need to navigate?

A

Local movements within familiar area

Local spatial responses to unfavourable conditions

Dispersal to new habitat

Regular, predictable movements to new areas; usually long-distance relative to home range (migration?)

Homing: return to a locality after intended movement or unintended movement (displacement / translocation)

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2
Q

Key definitions

A

Capacity to move: drift, muscle-powered locomotion, selective tidal stream transport

Directional cues:

-Orientation: is maintenance of the body position/alignment relative to an external cue

  • Piloting: use of local landmarks and spatial memory to reach a site (goal)
  • Navigation: ability to head towards and locate goal in unfamiliar territory, after moving in anew and unfamiliar direction
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3
Q

Simple orientation cues

A

Many animals show simple orientation responses that are fundamental to them remaining in or locating appropriate conditions

Kinesis – animal’s response proportional to intensity of stimulation

Orthokinesis – Increased stimulation results in increased speed of locomotion

Klinokinesis – Rate of direction changing increases as stimulus increases

Taxis – movement towards or away from stimulus– more useful for directed movements, and potentially used for finding suitable areas

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4
Q

Taxis

A

Example: Water Boatmen are positively phototaxic when they need air and negatively phototaxic once air is replenished

Many river fish are positively rheotactic – align and swim against the flow. This helps to retain position against current, but is also important for directing upriver migration, e.g. by adult salmon

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5
Q

Orientation mechanisms

A

Local movements and migrations may use an integration of appropriate orientation mechanisms

e.g. Orientation mechanisms demonstrated to occur in different life cycle stages of Oncorhynchus Pacific salmon
(see notes for diagram)

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6
Q

Is large-scale motor performance necessary for long-distance migration?

A

Not necessarily, it may be passive movement – Long distance migrations may be achieved by passive drift, with sensory capability and local orientation, especially ‘on arrival’

Example:
Migration of European and American eel leptocephali larvae achieved mostly passively on the Gulf Stream currents

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7
Q

Orientation and navigation cues

A

Landmarks

Celestial cues

Electromagnetic fields

Chemical cues

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8
Q

Landmarks

A

Heliconias butterfly return to the same roosts each night

Dragonflies hawk for prey and return to a number of selected resting sites

Rockpool fishes able to find their way around pool and relocate it based on rock positions etc.

Retinotopic cues - Many animals are adept at piloting
Animal moves until the viewed image of a landmark falls on the same retinal locations memorized during a previous visits.

Short distances: Digger wasps circle the nest surveying the nest entrance in relation to local landmarks. Tinbergen removed pine cones placed around digger wasp nest and noticed that they then found it hard to find the nest entrance.

Longer distances: Landmarks for example, wood ants use retinotopic learning over long distances; they memorize & walk parallel to a distant edge. When the wall’s height was changed, the ants’ paths consistently shifted toward a lowered wall and away from a raised wall.

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9
Q

Celestial cues

A

Sun and moon (and other stars)

Used by wide variety of animals; relative position of sun (or moon / star map), in some cases also direction of polarised light (still works in cloudy weather)

Many tests based on homing and displacement

e.g.Arthur Hasler’s experiments on homing by displaced white bass in Lake Mendota, USA showed strong homing to breeding site after experimental displacement when sunny, poor when cloudy.

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10
Q

Celestial cues: Sun compass: orientation in White Bass

A

White bass homed using sun compass orientation (with time correction), but orientation poorer when cloudy

Sun rises predictably in east, is at its azimuth at noon, sets in west

Body clock enables animals to take account of position and adjust bearing relative to sun

Note: orientation is not highly accurate, but is enough – piloting can then take over

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11
Q

Celestial cues: Sun compass: bee waggle dance

A

Karl von Frisch (1886-1982) showed bees can adjust their flight using a sun compass;

Bees are able to perfectly orientate with <1% of blue sky;

They use UV light -although it is dim, it is resistant to interference.

Number of waggles important for distance

Shape of dance important for altitude

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12
Q

Celestial cues: star compass: many bird species

A

Many birds migrate at night

Emlen worked on indigo buntings (migrate N in spring, S in autumn) and stellar orientation.

Designed Emlen funnel to measure migratory restlessness directionality at dusk

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13
Q

Celestial cues: Star compass: Dung beetles

A

Dung beetles use stellar orientation, especially light from the milky way, to orientate and roll their dung balls back to their burrows.

Equally able on moonless nights.

Lose orientation ability on cloudy nights.

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14
Q

Electromagnetic fields: geomagnetic cues

A

Major cue for large-scale spatial movements, especially important for long-distance navigation.

Flowing metal (esp. Fe) in Earth’s core creates electric currents –Earth’s rotation generates magnetic field

3 main potential magnetic cues :

1) Polarity –S to N (currently)
2) Angle of inclination (dip) of magnetic field lines –steeper near poles
3)Intensity of field –strongest at poles

Response to alteration of geomagnetic field demonstrated in many inverts & verts

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15
Q

Electromagnetic fields: build your own compass

A

Biogenic magnetite & maghemite (biologically secreted iron crystals - widely found in animals + some bacteria) – research by Kirschvink, Diebel etc on wide range of taxa. In specialised cells which link directly to nerve endings (= trigeminal nerves in vertebrates) passing to brain.

The brain builds a magnetic map used in subsequent navigation

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16
Q

Electromagnetic cues: Geomagnetic cues

A

Magnetic Compass (‘dip’ compass)

Robins kept in cages with altered magnetic fields orient in normal direction when magnetic field is normal, but also when it is reversed, they not detect polarity direction – just angle of dip.

When the field is opposite to normal they navigate at 180 degrees to normal

(Wiltschko & Wiltschko, 1972)

Chernetsov et al. 2008 study

17
Q

Electromagnetic cues: Geomagnetic cues: Reed Warblers

A

Reed warblers migrate North (N) in spring to Eurasian breeding grounds.

Showed that migrating warblers translocated 1000 km (displaced) E & placed in Emlen funnels orientated NW towards ‘home’ breeding grounds, while Control birds orientated NE towards same area .

Able to adjust for altered position to arrive at goal location –true bicoordinate navigation. Cutting trigeminal nerve prevented this - when the nerve was cut they were unable to navigate

(see diagram in notes)

18
Q

Celestial & electromagnetic cues: Moths

A

A wide range of invertebrates as well as vertebrates use cues

Moths navigate using the moon as a primary reference and calibrate that reference with their internal geomagnetic compass.

Every hour they alter their flight path by ~15 degrees to correct for the travel of the moon across the sky (the Earth’s rotation). - the nocturnal equivalent of a sun compass

Have a biological clock to account for time of day/night

On moonless nights they navigate solely with the geomagnetic compass.

This explains why moths crowd towards artificial lights

A Silver-Y moth (Autographa gamma) – migrates ~ 300 km per night, Europe, spring & autumn

Some moths also have iron crystals in their tissues that may help them with geo-navigation

19
Q

chemical cues: pheremones

A

Pheromones: chemicals produced by an animal which change the behaviour or development of other animals of the same species

Some pheromones are heterospecific – can affect other (usually closely related) species

Produced in small amounts often naturally occurring compounds highly volatile or require physical contact often highly specific often released under specific conditions secreted by exocrine glands. Often sex-specific.

Male moths exhibit ‘casting’ behaviour –differential reception of odour molecules across its two antennae (note the antennae are more developed in males) using this information it tracks the females pheremones to where she is waiting

20
Q

Chemical cues: pheremones/ stream chemicals? Home stream odour hypothesis in returning salmon

A

It has been observed that salmon return to the streams they hatched in to lay their eggs – but how?

100+ years of research on migration, homing and orientation in semelparous salmonids, especially Oncorhynchus spp.

Natal homing: Parent stream hypothesis (Buckland, 1880 –atlantic salmon research)

Home stream odour

-1950’s Hasler – morpholine experiments
- hypothesised that smolts ‘imprint’ chemical cues of their home stream)
Hasler used morpholine to artificially imprint the smolt in a fish farm and showed that the Salmon would return to specific pools according to where he had added morpholine – that they recognised from their early development

Pheromones / stream chemicals? Some evidence for both

Hiroshi Ueda theory: all rivers have unique ‘finger prints’ - different natural odours caused by amino acids amongst other chemicals

Geomagnetism also plays a role in navigation for homing in from long distances before scent can be identified

21
Q

Chemical cues: pheremones - Lamphreys

A

Lifecycle is similar to salmon as they migrate from river to sea. However, parasitic lamprey feed on host fish at sea so are often moved long distances from suitable reproductive habitat by hosts (which they attach to for feeding). This is whey they do not show natal homing behaviour and instead respond to pheromones of any Lamphrey streams to lay eggs.

Stream-dwelling lamprey larvae release bile acid pheromones (e.g. petromyzonol sulphate, PS) attractive (at 10-9M) to adults approaching coast and river mouths.

Enter streams with lamprey larvae, but NOT natal homing.

Mature males release keto-derivative of PS to attract female.

Vrieze & Sorensen (2001) & Li et al. (2002)
(see notes for diagrams)