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Glass knifefish Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia

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Presentation on theme: "Glass knifefish Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia"— Presentation transcript:

1 Glass knifefish Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia

2 What is an electric fish? Electric fishes: have the ability to generate an electric field---Electrogenic. Knifefish, Torpedo, Elephantnose Electrogenic are also electroreceptive. Fishes that are able to detect electric field but are not able to generate an electric field. Electroreceptive : Ability to detect electric field. Sharks, Skates, Rays and Catfish What is not an electric fish? Apteronotus albifrons Eigenmannia virescens

3 Electric fish species can be found both in the sea and in freshwater rivers of South America and Africa.

4 Electric fishes: (Based on the voltage of EOD) Weakly electric fish (several hundred millivolts) Strongly electric fish (several hundred volts)

5 Electric fishes: (Based on the discharge pattern) Pulse type: Brief electrical pulses followed by variable intervals of silence. Elephant nose (Gnathonemus petersii) Wave type: Sinusoidal with duration of electric pulses comparable to duration of interpulse intervals. Knifefish (Eigenmannia sp)

6 Electric Organs Myogenic: Derived from various types of muscles Neurogenic: Derived from modified spinal motor axons (oder Gymnotiformes) Number of electric organs may be one or more than one. Electrocytes are arranged in series. Simultaneous firing of electrocytes results in the electric organ discharges (EODs) which are emitted in the surrounding water. Composed of electrocytes

7 The regularity of the electric organ discharge is d etermined by an endogenous oscillator in medulla oblongata called the pacemaker nucleus (PN). Electric organ is innervated by electromotoneurons Innervation site has distinct evagination---stalk PN EO Electromotoneuron

8 Electroreceptors Specific sensory cell that mediates the perception of electric signal Senses own EOD EOD of other fishes Abiotic sources Electroreceptors are abundant in the head region Electroreceptors Ampullary Tuberous P type (Amplitude) T type (Phase) Mark Nelson

9 Electrolocation is the ability of electric fish to detect and localize objects around them. It allows electric fish to hunt and navigate in the absence of visual cues at night or in turbid water. Conducting object An object with higher or lower conduc- tivity than the surrounding water causes distortion of the electric field lines. This causes the area of the skin nearest to the object to have different voltage than the rest of the body, which the fish can monitor by its electroreceptors. Thus, it locates the object. Electric Current Electric organ

10 Jamming Avoidance Response (JAR) The most intensively studied behavior of electric fish is the JAR of high frequency wave type species. The fish’s ability to electrolocate is affected in the presence of another fish with similar EOD frequency. The two electric fields interfere with each other resulting in phase and amplitude modulation of each of the two electric signals. This impairs the fish’s ability to electrolocate. In order to avoid such detrimental interference of the two electric fields the fish shifts its own frequency away from that of its neighbor. This behavior is called JAR What is JAR ? Eigenmannia virescens

11 JAR leads to two distinct behavioral patterns If the neighbor’s EOD frequency is higher than the the fish’s own frequency then the fish lowers its EOD frequency. If the neighbor’s EOD frequency is lower than the the fish’s own frequency then the fish raises its EOD frequency BEFORE JAR f A =300Hz, f B =304Hz AFTER JAR f A =292Hz, f B =312Hz DF(frequency difference) = Neighbor(f) – Own(f) Lowers its frequency if DF=(+)ve Raises its frequency if DF=(-)ve Frequency shift evoked when DF < 20Hz

12 Silencing of electric organ with curare. EOD replaced by electric sine wave of similar amplitude and frequency Mimic of neighbor’s electric field Result: Correct jamming avoidance behavior Lowers its pacemaker frequency if DF=(+)ve Raises its pacemaker frequency if DF=(-)ve Do not tell much about the behavioral mechanism involved in determining the sign of DF.

13 Frequency of the EOD mimic was decreased to a frequency 50 Hz below the frequency of the pacemaker nucleus When confronted with neighbor’s EOD mimic it responded as if this 50 Hz lower frequency was its own frequency. Pacemaker (f) =100 Hz EOD mimic (f)= 50 Hz Neighbor’s EOD mimic (f)=54 Hz Uses the electrical field frequency rather than internal frequency of the pacemaker nucleus----- NO INTERNAL REFERENCE

14 Fish placed in two compartment chamber Pectoral region sealed No EOD could be detected by head region Jamming stimulus presented to the head No JAR JAR elicited when EOD leaked into head chamber Jamming signal entered the tail chamber Fish needs a mixture of its own signal and neighbor’s signal to execute JAR Electroreceptor

15 A Mimics of two EODs were added and presented. Electrical fields had different Frequency, but identical geometry NO VARIATION IN MIXING RATIO OVER BODY SURFACE----NO JAR Under natural situation electrical fields vary both in frequency and geometry VARIATION IN MIXING RATIO-----JAR

16 The amplitude and the phase of the mixed electric field signal is different from the amplitudes and the phases of the individual signals. Moreover, the amplitude and phase of the mixed signal are modulated over the body surface of the electric fish. By sensing this modulation of the amplitude and phase, the fish can determine if the other signal has a lower or higher frequency. Important requirements for JAR: 1. Absolute value of the difference in frequency less than 20 Hz 2. Mixing of signals 3. Variation in mixing ratio 4. Modulation of phase and amplitude of the mixed signal

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