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词条 Electric organ (biology)
释义

  1. Research history

  2. Evolution

  3. Electrocytes

     Firing 

  4. Location

  5. Electric organ discharge

  6. Further reading

  7. References

{{about|the organ found in electric fish|the musical instrument|electronic organ}}

In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue.[1] The electric discharge from this organ is used for navigation, communication, mating, defense and also sometimes for the incapacitation of prey.[2][3]

Research history

In the 1770s the electric organs of the torpedo and electric eel were the subject of Royal Society papers by Hunter, Walsh and Williamson. They appear to have influenced the thinking of Luigi Galvani and Alessandro Volta - the founders of electrophysiology and electrochemistry.[4]

In the 19th century, Charles Darwin discussed the electric organ in his Origin of Species as a likely example of convergent evolution: "But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other…I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings".[5]

Since the 20th Century, electric organs have received extensive study, for example Lissmann's 1951 paper[6] and his review of their function and evolution in 1958.[7]

Evolution

Electric organs have evolved at least six times in various teleost and elasmobranch fish.[8] Notably, they have convergently evolved in the African Mormyridae and South American Gymnotidae groups of electric fish. The two groups are distantly related, as they shared a common ancestor before the supercontinent Gondwana split into the American and African continents, leading to the divergence of the two groups. A whole-genome duplication event in the teleost lineage allowed for the neofunctionalization of the voltage-gated sodium channel gene Scn4aa which produces electric discharges.[8][9] Developmentally, most electric organs in electric fish are derived from skeletal muscle.

Electrocytes

Electrocytes, electroplaques or electroplaxes are cells used by electric eels, rays, and other fish for electrogenesis. They are flat disk-like cells. Electric eels have several thousand of these cells stacked, each producing 0.15 V. The cells function by pumping positive sodium and potassium ions out of the cell via transport proteins powered by adenosine triphosphate (ATP). Postsynaptically, electrocytes work much like muscle cells.{{clarify|date=March 2017}}{{citation needed|date=March 2017}} They have nicotinic acetylcholine receptors.

These cells are used in research because of their resemblance to nerve-muscle junctions.

The stack of electrocytes has long been compared to a voltaic pile, and may even have inspired the invention of the battery, since the analogy was already noted by Alessandro Volta.[4] While the electric organ is structurally similar to a battery, its cycle of operation is more like a Marx generator, in that the individual elements are slowly charged in parallel, then suddenly and nearly simultaneously discharged in series to produce a high voltage pulse.

Firing

To discharge the electrocytes at the correct time, the electric eel uses its pacemaker nucleus, a nucleus of pacemaker neurons. When an electric eel spots its prey, the pacemaker neurons fire and acetylcholine is subsequently released from electromotor neurons to the electrocytes. The electrocytes fire an action potential using the voltage-gated sodium channels on one or both sides of the electrocyte, depending on the complexity of the electric organ in that species. If the electrocyte has sodium channels on both sides, the depolarization caused by firing action potentials on one side of the electrocyte can cause the sodium channels on the other side of the electrocyte to fire as well.[10]

Location

In most fishes, electric organs are oriented to fire along the length of the body, usually lying along the length of the tail and within the fish's musculature, with smaller accessory electric organs in the head. However, there are some exceptions; in stargazers and in rays the electric organs are oriented along the dorso-ventral (up-down) axis. In the electric torpedo ray, the organ is near the pectoral muscles and the gills (see the image). The stargazer's electric organs lie between the mouth and the eye. In the electric catfish, the organs are located just below the skin and encase most of the body like a sheath.

Electric organ discharge

Electric organ discharge (EOD) is the electric field generated by the organs of animals including electric fish. In some cases the electric discharge is strong and is used for protection from predators; in other cases it is weak and it is used for navigation and communication.[11] Communicating through EODs occurs when a fish uses its own electroreceptors to sense the electric signals of a nearby fish.[12] Electric fish navigate by detecting distortions in their electrical field by using their cutaneous electroreceptors.[13][14][15] Electric organ discharges influence mate choice in weakly electric fish, as females have been shown to be attracted to electric discharge characteristics of conspecific males.[3]

Further reading

  • Review Article on the molecular evolution of the electric organ.[16]
  • Phylogeny of weakly electric fishes.[17][18]
  • Comprehensive overview of electric organ function and evolution in weakly electric fishes.[19]
  • Succinct Science article describing differences in gene expression between sarcomeres and electrocytes of electric organs.[20]

References

1. ^{{cite journal|last=Kramer|first=Bernd|title=Electroreception and communication in fishes|journal=Progress in Zoology|year=1996|volume=42|url=http://epub.uni-regensburg.de/2108/1/ubr00728.pdf}}
2. ^{{Cite journal |author=Castello, M. E., A. Rodriguez-Cattaneo, P. A. Aguilera, L. Iribarne, A. C. Pereira, and A. A. Caputi |title=Waveform generation in the weakly electric fish Gymnotus coropinae (Hoedeman): the electric organ and the electric organ discharge |journal=Journal of Experimental Biology |volume=212 |year=2009 |pages=1351–1364 |doi=10.1242/jeb.022566 |issue=9 |pmid=19376956}}
3. ^1 {{Cite journal |author=Feulner, P. G., M. Plath, J. Engelmann, F. Kirschbaum, R. Tiedemann |title=Electrifying love: electric fish use species-specific discharge for mate recognition |journal=Biology Letters |volume=5 |year=2009 |pages=225–228}}
4. ^1 Alexander Mauro, "The role of the voltaic pile in the Galvani-Volta controversy concerning animal vs. metallic electricity" in Journal of the History of Medicine and Allied Sciences, volume XXIV, number 2, April, 1969 available online at jhmas.oxfordjournals.org/cgi/reprint/XXIV/2/140.pdf
5. ^{{Cite book |title=On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. |last=Darwin, C. |year=1859 |publisher=John Murray |location=London |isbn=978-1-4353-9386-8 }}
6. ^{{Cite journal |author=Lissmann, H. W. |title=CONTINUOUS ELECTRICAL SIGNALS FROM THE TAIL OF A FISH, GYMNARCHUS-NILOTICUS CUV |journal=Nature |volume=167 |year=1951 |pages=201–202 | doi = 10.1038/167201a0 | pmid=14806425 |issue=4240}}
7. ^{{Cite journal |author= Lissmann, H. W. |title=ON THE FUNCTION AND EVOLUTION OF ELECTRIC ORGANS IN FISH |journal=Journal of Experimental Biology |volume=35 |year=1958 |page=156–& }}
8. ^{{Cite journal |author=Gallant, J. R., L. L. Traeger, J. D. Volkening, H. Moffett, P. H. Chen, C. D. Novina, G. N. Phillips|display-authors=etal|title=Genomic basis for the convergent evolution of electric organs |journal=Science |volume=344 | year=2014 |pages=1522–1525}}
9. ^{{Cite journal |author=Arnegard, M. E., D. J. Zwickl, Y. Lu, H. H. Zakon |title=Old gene duplication facilitates origin and diversification of an innovative communication system-twice |journal=Proceedings of the National Academy of Sciences |volume=107 |year=2010}}
10. ^{{Cite journal |author=Salazar, V. L., R. Krahe, J. E. Lewis |title=The energetics of electric organ discharge generation in gymnotiform weakly electric fish |journal=Journal of Experimental Biology |volume=216 |year=2013 |pages=2459–2468}}
11. ^Caputi, A. A., B. A. Carlson, and O. Macadar. 2005. Electric organs and their control. Pages 410-451 in T. H. Bullock, C. D. Hopkins, A. N. Popper, and R. R. Fay, eds. Electroreception. New York.
12. ^{{cite journal | author = Crampton W. G. R., Davis J. K., Lovejoy N. R., Pensky M. | year = 2008 | title = Multivariate classification of animal communication signals: A simulation-based comparison of alternative signal processing procedures using electric fishes | url = | journal = Journal of Physiology-Paris | volume = 102 | issue = 4–6| pages = 304–321 | doi=10.1016/j.jphysparis.2008.10.001| pmid = 18984042 }}
13. ^Bastian J. 1986. Electrolocation: behavior, anatomy, and physiology. Pages 577-612 in T. H. Bullock and W. Heiligenberg, eds. Electroreception. New York.
14. ^{{cite journal | author = Aguilera P. A., Caputi A. A. | year = 2003 | title = Electroreception in G. carapo: detection of changes in waveform of the electrosensory signals | url = | journal = Journal of Experimental Biology | volume = 206 | issue = 6| pages = 989–998 | doi=10.1242/jeb.00198}}
15. ^Pereira, A. C., and A. A. Caputi. 2010. Imaging in Electrosensory Systems. Interdisciplinary Sciences-Computational Life Sciences 2:291-307.
16. ^1 {{Cite journal |author=Zakon, H. H., D. J. Zwickl, Y. Lu, and D. M. Hillis |title=Molecular evolution of communication signals in electric fish |journal=Journal of Experimental Biology |volume=211 |year=2008 |pages=1814–1818 |doi=10.1242/jeb.015982 |pmid=18490397 |issue=11}}
17. ^{{Cite journal |author=Lavoue, S., R. Bigorne, G. Lecointre, and J. F. Agnese |title=Phylogenetic relationships of mormyrid electric fishes (Mormyridae; Teleostei) inferred from cytochrome b sequences |journal=Molecular Phylogenetics and Evolution |volume=14 |year=2000 |pages=1–10 |doi=10.1006/mpev.1999.0687 |pmid=10631038 |issue=1 }}
18. ^{{cite journal | author = Lavoué S., Miya M., Arnegard M. E., Sullivan J. P., Hopkins C. D., Nishida M. | year = 2012 | title = Comparable ages for the independent origins of electrogenesis in African and South American weakly electric fishes | url = | journal = PLoS ONE | volume = 7 | issue = 5| page = e36287 | doi=10.1371/journal.pone.0036287| pmid = 22606250 | pmc = 3351409 }}
19. ^{{Cite journal |author=Kawasaki, M. |title=Evolution of Time-Coding Systems in Weakly Electric Fishes |journal=Zoological Science |volume=26 |year=2009 |pages=587–599 |doi=10.2108/zsj.26.587 |pmid=19799509 |issue=9}}
20. ^{{Cite journal |author=Gallant, J. R., L. L. Traeger, J. D. Volkening, H. Moffett, P. H. Chen, C. D. Novina, G. N. Phillips, R. Anand, G. B. Wells, M. Pinch, R. Guth, G. A. Unguez, J. S. Albert, H. H. Zakon, M. P. Samanta, and M. R. Sussman |title=Genomic basis for the convergent evolution of electric organs |year=2014|volume=344 |issue=6191 |pages=1522–1525 |doi=10.1126/science.1254432 |pmid=24970089 |pmc=5541775 |journal=Science}}
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2 : Fish anatomy|Electric fish
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