In biology, the electric organ is a muscular organ (more accurately, derived from muscle [1] ) common to all electric fish used for the purposes of creating an electric field; a behavior used for navigation, communication and also sometimes for the incapacitation of prey.[2]
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Research History
Darwin, in The Origin of Species, marveled at the wonder of the electric organ's evolution, saying "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"[3].
Other than being mentioned by Darwin, however, the electric organ was seldom studied until its behavior was documented in 1951 [4] and eventually characterized by H. W. Lissmann in 1958 [5].
Electrocytes
Electrocytes, electroplaques or electroplaxes are cells used by rays, electric eels and other electric fish for electrogenesis and electroreception. They are flat disk-like cells that are positively charged on one side and negatively charged on the other. Electric eels have several thousand of these cells stacked, each producing 0.15V. The cells function by pumping positive sodium and potassium ions out of the cell via transport proteins powered by ATP. Postsynaptically, electrocytes work much like muscle cells. They have nicotinic acetylcholine receptors. These cells are used in research because of their resemblance to nerve-muscle junctions.
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, resulting in an electric organ discharge.
Location
In the electric Torpedo Ray, electroplaxes are found near the pectoral muscles and the gills. In most other fishes, they are found near the tail. In one fish genus, the electric catfish Malapterurus, the electric organs are not made of individual electroplaxes, but are built up from charges of the epithelium, specifically the skin.[6]
Electric Organ Discharge
Electric organ discharge (EOD) is the electric discharge 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.
Further Peer-Reviewed Reading
Review Article on the molecular evolution of the electric organ.[1]
Phylogeny of weakly electric fishes.[7]
Comprehensive overview of electric organ function and evolution in weakly electric fishes.[8]
References
- ^ a b Zakon, H. H., D. J. Zwickl, Y. Lu, and D. M. Hillis (2008). "Molecular evolution of communication signals in electric fish". Journal of Experimental Biology 211: 1814–1818. doi:.
- ^ Castello, M. E., A. Rodriguez-Cattaneo, P. A. Aguilera, L. Iribarne, A. C. Pereira, and A. A. Caputi (2009). "Waveform generation in the weakly electric fish Gymnotus coropinae (Hoedeman): the electric organ and the electric organ discharge". Journal of Experimental Biology 212: 1351–1364. doi:.
- ^ Darwin, C. (1859). On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life.. London: John Murray.
- ^ Lissmann, H. W. (1951). "CONTINUOUS ELECTRICAL SIGNALS FROM THE TAIL OF A FISH, GYMNARCHUS-NILOTICUS CUV". Nature 167: 201–202.
- ^ Lissmann, H. W. (1958). "ON THE FUNCTION AND EVOLUTION OF ELECTRIC ORGANS IN FISH". Journal of Experimental Biology 35: 156-&.
- ^ Hollmann, M., J. Engelmann, and G. von der Emde (2008). "Distribution, density and morphology of electroreceptor organs in mormyrid weakly electric fish: anatomical investigations of a receptor mosaic". Journal of Zoology 276: 149–158. doi:.
- ^ Lavoue, S., R. Bigorne, G. Lecointre, and J. F. Agnese (2000). "Phylogenetic relationships of mormyrid electric fishes (Mormyridae; Teleostei) inferred from cytochrome b sequences". Molecular Phylogenetics and Evolution 14: 1–10.
- ^ Kawasaki, M. (2009). "Evolution of Time-Coding Systems in Weakly Electric Fishes". Zoological Science 26: 587–599. doi:.
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