electrosensation in electric fish Flashcards
(31 cards)
Different types of electric sense: passive
passive sense (detect external electric fields):
- animate: gills, muscle, heart
- inanimate: earths geomagnetic field
25% of all fish
Use Ampullary receptors
Different types of electric sense: active
Active sense (detect perturbation in electric field emitted by the fish itself):
- animate: predators, prey
- inanimate: anything with electrical conductivity different to the water
All weekly electric fish and some strongly electric fish
Rquires tuberous receptors and an electric organs
Can detect:
- location
- Conductance
- Capacitance
- Distance
Generate a somatotropin map of the electrosensitive body surface
electric fish -
Send out electrical files and can detect any distortions tell them about the environment - can detect anything with a different electrical field
Specialisations for electro-sensation:
- ability to detect electric fields in surrounding medium (specialised sensory structures, brain regions and body shape)
- ability to produce and emit electric field (specialised electric organ controlled by a specialised motor nucleus in the brain stem)
- modified behaviours related to use of electric signals for prey detection and communication
Two types of weakly electric fish:
Gymnotiforms and mormyriformes
- electric sense very similar but these fish evolved separately (common ancestor did not possess electric sense
Gymnotiformes -
South America
E.g. knife fish - specialised tail
Almost exclusively wave type
Generation of electric discharge - electric organ discharges (EOD):
Electric organs usually consist of modified muscle cells (electrocytes) - excitation contraction coupling is disabled =no contraction
Flattened muscle electrocyte cells are stacked to form electroplaques - surrounded by an insulating connective sheath (so electrocurrent doesn’t escape into environment)
Motor neurones innervate one side of the muscle fibre = produces action potential causes electrocytes to become excited allowing current to flow through into environment
Mormyriformes -
Africa
E.g. elephant fish (specialised trunk muscles)
Almost exclusively pulse type
Strongly electric fish electric organ discharge:
monopolar - best for stunning prey
Iso voltage curves -
Form a map of voltage (governed by shape of fish)
Current flows (at right angles to voltage) from one end of fish to the other end
Weakly electric fish electric organ discharge:
Bipolar or more complex waveforms
electro-receptive sense organs:
Two types: Ampullary and tuberous
- All electroreceptors are hair cells (similar to mechanoreceptors)
- they form part of the octavo-lateral sensory system - which includes the receptors for hearing, eqbm, gravity/rotation and water currents
Ampullary receptors:
Have a jelly-filled opening (canal) through the epidermis to the outside
- Low resistance, high sensitivity to low frequencies
Found in many fish - weakly electric fish, rays and sharks
Very sensitive to weak electric field gradients
Sensory neurones are spontaneously active
Respond only to low frequency signals
Tuberous receptors:
Canal loosely ‘plugged’ with epidermal cells…
- 100x less sensitive
- only respond to high frequencies
- only found in electric fish
Respond to the discharged of electric organs
Two types: time markers and amplitude condors - these receptors together permit…
- detection of EODs generated by conspecifics and thus electrocommunication
- the presence of objects in the environment and thus electrolocation
Time marker tuberous electroreceptors:
- High sensitivity
- Fixed latency (fire at precise time)
- detect the timing of the fish’ own EOD or that of a conspecific
- fire a single action potential per EOD
Amplitude condors tuberous electroreceptors:
- Low overall sensitivity but very high sensitivity to tiny changes in the amplitude of a fish’ own EOD
- bursts of spikes in which the latency of the first spike signals amplitude (higher amplitude = shorter latency)
Receptors in mormyrid fish from Africa (elephantfish)…
Time coders = knollenorgane (K-receptors)
Amplitude coders = mormyromasts (D-receptors) - these are important in active object location
Different parameters of the ‘electric image’ provide different info about an object…
- the location of receptors detecting a distortion indicates the location of the object relative to the body
- the sign of the distortion indicates conductance
- changes in waveform or timing indicate capacitance
Distance estimation experiment:
Electrodes placed near body of fish to see what different objects ‘look like’ to the fish’ sensory receptors at different distances
Conductors - have increased EOD amplitude
Insulators - have decreased EOD amplitude
Shorter distance = small image, Higher contrast = larger signal
Therefore can work out distance despair of size/shape of object
Proposed mechanism for depth perception in weakly electric fish =
Use a single stationary array of receptors without resorting to temporal or spectral measurements
Capacitance estimation:
Capacitance = electrical property of material that store charge
Living organism = high capacitance
Inanimate objects = low capacitance
= capacitance is useful in distinguishing other organisms from environment
Receptors in gymnotid fish from South America (knifefish)…
Pulse fish:
time coders = M receptors
Amplitude coders = B (burst) receptors
Wave fish:
Time coders = T (time) receptors
Amplitude coders = P (probability) receptors
in pulse type mormyrids capacitance…
modifies the shape, but not the timing of EOD pulses
- receptors detect waveform distortion - responses of A and B cells are compared to allow fish to distinguish between resistive and capacitance objects
in wave type gymnotids capacitance…
modifies the timing (phase) of the field relative to the emission
- T type receptors detect timing distortions, by comparing distortions at receptors all over the body the fish can localise capacitive objects
