Electroreception and electrogenesis

Most bony fishes have secondarily lost their ampullae of Lorenzini, but other non-homologous electroreceptors have repeatedly evolved, including in two groups of mammals, the monotremes (platypus and echidnas) and the cetaceans (Guiana dolphin).

[4][5] In 1921, the German anatomist Viktor Franz described the knollenorgans (tuberous organs) in the skin of the elephantfishes, again without knowledge of their function as electroreceptors.

In 1949, the Ukrainian-British zoologist Hans Lissmann noticed that the African knife fish (Gymnarchus niloticus) was able to swim backwards at the same speed and with the same dexterity around obstacles as when it swam forwards, avoiding collisions.

[10][11] Passive electroreception usually relies upon ampullary receptors such as ampullae of Lorenzini which are sensitive to low frequency stimuli, below 50 Hz.

Active electroreception typically has a range of about one body length, though objects with an electrical impedance similar to that of the surrounding water are nearly undetectable.

[22] When two glass knifefishes (Sternopygidae) come close together, both individuals shift their discharge frequencies in a jamming avoidance response.

The cost to males is reduced by a circadian rhythm, with more activity coinciding with night-time courtship and spawning, and less at other times.

The electroreceptive African sharptooth catfish (Clarias gariepinus) may hunt the weakly electric mormyrid, Marcusenius macrolepidotus in this way.

[25] This has driven the prey, in an evolutionary arms race, to develop more complex or higher frequency signals that are harder to detect.

These evolved from the mechanical sensors of the lateral line, and exist in cartilaginous fishes (sharks, rays, and chimaeras), lungfishes, bichirs, coelacanths, sturgeons, paddlefishes, aquatic salamanders, and caecilians.

Ampullae of Lorenzini appear to have been lost early in the evolution of bony fishes and tetrapods, though the evidence for absence in many groups is incomplete and unsatisfactory.

[27] Actively electrolocating fish are marked with a small yellow lightning flash and their characteristic discharge waveforms.

Selachimorpha (sharks) Torpediniformes (electric rays) other rays Rajidae (skates) Coelacanths Lungfishes (aquatic salamanders, caecilians; others: lost) (platypus, echidna) (Guiana dolphin) bichirs, reedfishes sturgeons, paddlefishes elephantfishes African knifefish

Stargazers Sharks and rays (Elasmobranchii) rely on electrolocation using their ampullae of Lorenzini in the final stages of their attacks, as can be demonstrated by the robust feeding response elicited by electric fields similar to those of their prey.

[30][31][32][33] Two groups of teleost fishes are weakly electric and actively electroreceptive: the Neotropical knifefishes (Gymnotiformes) and the African elephantfishes (Notopteroidei), enabling them to navigate and find food in turbid water.

While the electroreceptors in fish and amphibians evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves.

By making short quick head movements called saccades, platypuses accurately locate their prey.

Western long-beaked echidnas feed on earthworms in leaf litter in tropical forests, wet enough to conduct electrical signals well.

[39] Experiments have shown that echidnas can be trained to respond to weak electric fields in water and moist soil.

The hairless vibrissal crypts on the rostrum of the Guiana dolphin (Sotalia guianensis), originally associated with mammalian whiskers, are capable of electroreception as low as 4.8 μV/cm, sufficient to detect small fish.

The elephantnose fish is a weakly electric mormyrid fish which generates an electric field with its electric organ and then uses its electroreceptive knollenorgans and mormyromasts to locate nearby objects by the distortions they cause in the electric field. [ 1 ]
Hans Lissmann discovered electroreception in 1950 through his observations of Gymnarchus niloticus . [ 2 ]
Electric eels create electric fields powerful enough to stun prey using modified muscles . Some weakly electric knifefishes appear to mimic the electric eel's discharge patterns; this may be Batesian mimicry , to deceive predators that they are too dangerous to attack. [ 20 ]
The platypus is a monotreme mammal that has secondarily acquired electroreception. Its receptors are arranged in stripes on its bill, giving it high sensitivity to the sides and below; it makes quick turns of its head as it swims to detect prey. [ 37 ] [ 38 ]