Jamming avoidance response
The jamming avoidance response is a behavior of some species of
The behavior has been most intensively studied in the
Discovery
The jamming avoidance response (JAR) was discovered by Akira Watanabe and Kimihisa Takeda in 1963. The fish they used was an unspecified species of Eigenmannia, which has a quasi-sinusoidal wave discharge of about 300 Hz. They found that when a sinusoidal electrical stimulus is emitted from an electrode near the fish, if the stimulus frequency is within 5 Hz of the fish's electric organ discharge (EOD) frequency, the fish alters its EOD frequency to increase the difference between its own frequency and the stimulus frequency. Stimuli above the fish's EOD frequency push the EOD frequency downwards, while frequencies below that of the fish push the EOD frequency upwards, with a maximum change of about ±6.5 Hz.[1] This behavior was given the name "jamming avoidance response" several years later in 1972, in a paper by Theodore Bullock, Robert Hamstra Jr., and Henning Scheich.[2]
In 1975,
Behavior
Eigenmannia and other weakly electric fish use
If a neighboring sinusoidal electric field is discharging close to the fish's EOD frequency, it causes interference which results in sensory confusion in the fish and sufficient jamming to prevent it from electrolocating effectively.[5] Eigenmannia typically are within the electric field range of three to five other fish of the same species at any time. If many fish are located near each other, it is beneficial for each fish to distinguish between their own signal and those of others; this can be done by increasing the frequency difference between their discharges. Therefore, it seems to be the function of the JAR to avoid sensory confusion among neighboring fish.[6]
To determine how close the stimulus frequency is to the discharge frequency, the fish compares the two frequencies using its electroreceptive organs, rather than comparing the discharge frequency to an internal pacemaker; in other words, the JAR relies only on sensory information. This was determined experimentally by silencing a fish's electric organ with curare, and then stimulating the fish with two external frequencies. The JAR, measured from the electromotor neurons in the spinal cord, depended only on the frequencies of the external stimuli, and not on the frequency of the pacemaker.[7]
Neurobiology
Pathway in Eigenmannia (Gymnotiformes)
Most of the JAR pathway in the South American Gymnotiformes has been worked out using Eigenmannia virescens as a model system.[8][9]
Sensory coding
When the stimulus frequency and discharge frequency are close to each other, the two amplitude-time waves undergo
Gymnotiforms have two classes of electroreceptive organs, the
Processing in the brain
The time-coding T-units converge onto
Spherical cells and pyramidal cells then project to the
Output
Sign-selective cells input into the nucleus electrosensorius in the diencephalon, which then projects onto two different pathways. Neurons selective for a positive difference (stimulus greater than EOD) stimulate the prepacemaker nucleus, while neurons selective for a negative difference (stimulus less than EOD) inhibit the sublemniscal prepacemaker nucleus. Both prepacemaker nuclei send projections to the pacemaker nucleus, which ultimately controls the frequency of the EOD.[8]
Pathway in Gymnarchus (Osteoglossiformes)
The neural pathway of JAR in Gymnarchus is nearly identical to that of the Gymnotiformes, with a few minor differences. S-units in Gymnarchus are time coders, like the T-units in Gymnotiformes. O-units code the signal's intensity, like P-units in Gymnotiformes, but respond over a narrower range of intensities. In Gymnarchus, phase differences between EOD and stimulus are calculated in the electrosensory lateral line lobe rather than in the torus semicircularis.[11]
Phylogeny and evolution of weakly electric fish
There are two main
Vertebrates |
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See also
References
Further reading
- Springer Verlag.
- Heiligenberg, W. (1990) Electric Systems in Fish. Synapse 6:196-206.
- Heiligenberg, W. (1991) Neural Nets in Electric fish. MIT Press: Cambridge, Massachusetts.
- Kawasaki, M. (2009) Evolution of time-coding systems in weakly electric fishes. Zoological Science 26: 587-599.