Article courtesy Kenneth C. Catania with Nature Communications.
Electric eels (Electrophorus electricus) are legendary for their ability to incapacitate fish, humans, and horses with hundreds of volts of electricity. The function of this output as a weapon has been obvious for centuries but its potential role for electroreception has been overlooked. Here it is shown that electric eels use high-voltage simultaneously as a weapon and for precise and rapid electrolocation of fast-moving prey and conductors. Their speed, accuracy, and high-frequency pulse rate are reminiscent of bats using a ‘terminal feeding buzz’ to track insects. Eel’s exhibit ‘sensory conflict’ when mechanosensory and electrosensory cues are separated, striking first toward mechanosensory cues and later toward conductors. Strikes initiated in the absence of conductors are aborted. In addition to providing new insights into the evolution of strongly electric fish and showing electric eels to be far more sophisticated than previously described, these findings reveal a trait with markedly dichotomous functions.
Few species have garnered more historical interest and investigation than electric eels. First used as a prized source of electricity in experiments by Walsh1, Humboldt2 and Faraday3 they later played a pivotal role in the isolation of the acetylcholine receptor4 and determining the structure of voltage-gated sodium channels5. For centuries it was obvious that eels used their high voltage as a weapon, but how it evolved remained a mystery to Darwin6 who considered electric organs under ‘Special Difficulties of the Theory of Natural Selection’. The difficulty in the case of strongly electric fish was that no function had been ascribed to the smaller electric organs that were present in many extant species and that must have been present in eel ancestors. The discovery in the 1950s that weakly electric fish generate minute electric fields as part of an elaborate sensory system7 solved this longstanding mystery. Weakly electric fish, including close relatives of the electric eel, are able to discriminate objects with electricity by monitoring distortions in a self-generated electric field surrounding their body8, 9, 10, 11. Electric eels retain this low-voltage sensory system12, 13 including a weak electrical discharge and corresponding electroreceptors (Fig. 1). But the possibility that the eel’s high-voltage discharge plays a sensory role has been overlooked.
(a) Eel colourized to show electroreceptors (magenta) and mechanoreceptors-neuromast canals (blue). (b) The weak, low-voltage output used for electrolocation and the high-voltage, high-frequency output used as a weapon. (c) Schematic illustration of electrolocation based on the convergence of electric field lines on the eel’s skin (arrow).
The experiments described below address this question by taking advantage of the binary nature of the eel’s hunting behaviour. Eels emit the low-voltage weak output while searching and the high-voltage output when striking. Strikes begin with high-voltage volley onset (≈400 Hz, Fig. 1) followed milliseconds later by rapid head translation, and culminate in suction-feeding when the target is reached. Here experiments show that eels can find and track conductors using these high-voltage volleys without the aid of vision, mechanosensation, chemoreception or biogenic electric fields.
To see more of the in-depth study, visit Nature Communications.
