![Electroreception system in Elephantfish](https://upload.wikimedia.org/wikipedia/commons/5/54/Electroreception_system_in_Elephantfish.svg)
Electroreception and electrogenesis are the closely-related biological abilities to perceive
electrical
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
stimuli and to generate
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
s. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better
conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly
electric fish, the
Gymnotiformes (knifefishes) and the
Mormyridae
The Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are a family of weakly electric freshwater fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order with around 2 ...
(elephantfishes), and by ''
Gymnarchus
''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – is an electric fish, and the only species in the genus ''Gymnarchus'' and the family Gymnarchida ...
niloticus'', the African knifefish. An electric fish generates an electric field using an
electric organ
An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the pump organ, harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has sinc ...
,
modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the
electric eel
The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the
electric ray
The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, depending ...
, electrolocate passively. The
stargazers are unique in being strongly electric but not using electrolocation.
The electroreceptive
ampullae of Lorenzini evolved early in the history of the vertebrates; they are found in both
cartilaginous fishes such as
shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...
s, and in
bony fishes such as
coelacanth
The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...
s and
sturgeon
Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...
s, and must therefore be ancient. Most bony fishes have secondarily lost their ampullae of Lorenzini, but other non-
homologous electroreceptors have repeatedly evolved, including in two groups of
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, the
monotremes (
platypus
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...
and
echidna
Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...
s) and the
cetacea
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
ns (
Guiana dolphin
The Guiana dolphin (''Sotalia guianensis''), also known as the estuarine dolphin or costero, is a dolphin found in the coastal waters to the north and east of South America, and east of Central America. It is a member of the oceanic dolphin fami ...
).
History
![Gymnarchus niloticus005 (cropped)](https://upload.wikimedia.org/wikipedia/commons/2/2d/Gymnarchus_niloticus005_%28cropped%29.JPG)
In 1678, while doing dissections of sharks, the Italian physician
Stefano Lorenzini
Stefano is the Italian form of the masculine given name Στέφανος (Stefanos, Stephen). The name is of Greek origin, Στέφανος, meaning a person who made a significant achievement and has been crowned. In Orthodox Christianity the ach ...
discovered organs on their heads now called ampullae of Lorenzini. He published his findings in ''Osservazioni intorno alle torpedini''. The electroreceptive function of these organs was established by R. W. Murray in 1960.
In 1921, the German anatomist Viktor Franz described the
knollenorgan
A Knollenorgan is an electroreceptor in the skin of weakly electric fish of the family Mormyridae (Elephantfish) from Africa. The structure was first described by Viktor Franz (1921), a German anatomist unaware of its function. They are named afte ...
s (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. He demonstrated in 1950 that the fish was producing a variable electric field, and that the fish reacted to any change in the electric field around it.
[ Lissmann, Hans.]
Continuous Electrical Signals from the Tail of a Fish, ''Gymnarchus Niloticus'' Cuv
, in: ''Nature
Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
'', 167, 4240 (1951), pp. 201–202.
*
The Mechanism of Object Location in ''Gymnarchus Niloticus'' and Similar Fish
, in: ''Journal of Experimental Biology
''Journal of Experimental Biology'' (formerly ''The British Journal of Experimental Biology)'' is a peer-reviewed scientific journal in the field of comparative physiology and integrative biology. It is published by The Company of Biologists. Th ...
'', 35 (1958), pp. 451–486. (with Ken E. Machin)
*
The Mode of Operation of the Electric Receptors in ''Gymnarchus Niloticus''
, in: ''Journal of Experimental Biology
''Journal of Experimental Biology'' (formerly ''The British Journal of Experimental Biology)'' is a peer-reviewed scientific journal in the field of comparative physiology and integrative biology. It is published by The Company of Biologists. Th ...
'' 37:4 (1960), pp. 801–811. (with Ken E. Machin)
*
Electric Location by Fishes
, in: ''Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it i ...
'', 208, pp 50–59, March 1963.
Electrolocation
Electroreceptive animals use the sense to locate objects around them. This is important in
ecological niche
In ecology, a niche is the match of a species to a specific environmental condition.
Three variants of ecological niche are described by
It describes how an organism or population responds to the distribution of resources and competitors (for ...
s where the animal cannot depend on vision: for example in caves, in murky water, and at night. Electrolocation can be passive, sensing electric fields such as those generated by the muscle movements of buried prey, or active, the electrogenic predator generating a weak electric field to allow it to distinguish between conducting and non-conducting objects in its vicinity.
Passive electrolocation
In passive electrolocation, the animal senses the weak
bioelectric fields generated by other animals and uses it to locate them. These electric fields are generated by all animals due to the activity of their nerves and muscles. A second source of electric fields in fish is the
ion pump
An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump which operates by sputtering a metal getter. Under ideal conditions, ion pumps are capable of reaching pressures as low as 10−11 mbar. An ion pump first ionizes ga ...
associated with
osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration o ...
at the
gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
membrane. This field is modulated by the opening and closing of the mouth and gill slits.
Passive electroreception usually relies upon ampullary receptors such as ampullae of Lorenzini which are sensitive to low frequency stimuli, below 50 Hz. These receptors have a jelly-filled canal leading from the sensory receptors to the skin surface.
Active electrolocation
In active electrolocation,
the animal senses its surrounding environment by generating weak
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
s (electrogenesis) and detecting distortions in these fields using electroreceptor organs. This electric field is generated by means of a specialised
electric organ
An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the pump organ, harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has sinc ...
consisting of modified muscle or nerves.
Animals that use active electroreception include the
weakly electric fish
An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family. Electric fish, although a small minority, in ...
, which either generate small electrical pulses (termed "pulse-type"), as in the Mormyridae, or produce a quasi-
sinusoidal
A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in m ...
discharge from the electric organ (termed "wave-type"), as in the Gymnotidae.
Many of these fish, such as ''
Gymnarchus
''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – is an electric fish, and the only species in the genus ''Gymnarchus'' and the family Gymnarchida ...
'' and ''
Apteronotus'', keep their body rather rigid, swimming forwards or backwards with equal facility by undulating
fin
A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
s that extend most of the length of their bodies. Swimming backwards may help them to search for and assess prey using electrosensory cues. Experiments by Lannoo and Lannoo in 1993 support Lissmann's proposal that this style of swimming with a straight back works effectively given the constraints of active electrolocation. ''Apteronotus'' can select and catch larger ''
Daphnia
''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembl ...
'' water fleas among smaller ones, and they do not discriminate against artificially-darkened water fleas, in both cases with or without light.
These fish create a potential usually smaller than one
volt
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827).
Defi ...
(1 V). Weakly electric fish can discriminate between objects with different
resistance and
capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
values, which may help in identifying objects. Active electroreception typically has a range of about one body length, though objects with an
electrical impedance
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the comp ...
similar to that of the surrounding water are nearly undetectable.
Active electrolocation relies upon tuberous electroreceptors which are sensitive to high frequency (20-20,000
Hz) stimuli. These receptors have a loose plug of
epithelial
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
cells which
capacitively couples the sensory receptor cells to the external environment.
Elephantfish (Mormyridae) from Africa have tuberous electroreceptors known as
Knollenorgans and Mormyromasts in their skin.
Elephantfish emit short pulses to locate their prey.
Capacitative and
resistive
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels ...
objects affect the electric field differently, enabling the fish to locate objects of different types within a distance of about a body length. Resistive objects increase the amplitude of the pulse; capacitative objects introduce distortions.
File:Electroreception of Capacitative and Resistive Objects in Elephantfish.svg, Electrolocation of capacitative and resistive objects in elephantfish. The fish emits brief pulses from its electric organ; its electroreceptors detect signals modified by the electrical properties of the objects around it.
File:Scene analysis in electroreception coloured.jpg, For the elephantfish, the electric organ in the tail (blue) generates an electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
(cyan). This is sensed by electroreceptors in the skin, including two electric pits (foveas) to actively search and inspect objects. Shown are the field distortions created by two different types of objects: a plant that conducts better than water (green) and a non-conducting stone (brown).
The
Gymnotiformes, including the
glass knifefish
Glass knifefishes are fishes in the family Sternopygidae in the order Gymnotiformes. Species are also known as rattail knifefishes.
These fishes inhabit freshwater streams and rivers in Panama and South America. Many sternopygid species are sp ...
(Sternopygidae) and the
electric eel
The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
(Gymnotidae), differ from the Mormyridae in emitting a continuous wave, approximating a sine wave, from their electric organ. As in the Mormyridae, the generated electric field enables them to discriminate accurately between capacitative and resistive objects.
Electrocommunication
![Sidderaal (4039238527)](https://upload.wikimedia.org/wikipedia/commons/1/1d/Sidderaal_%284039238527%29.jpg)
Weakly electric fish can communicate by modulating the electrical
waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electro ...
they generate. They may use this to attract mates and in territorial displays. Electric catfish frequently use their electric discharges to ward off other species from their shelter sites, whereas with their own species they have ritualized fights with open-mouth displays and sometimes bites, but rarely use electric organ discharges.
When two glass knifefishes (Sternopygidae) come close together, both individuals shift their discharge frequencies in a
jamming avoidance response
The jamming avoidance response is a behavior of some species of weakly electric fish. It occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish shifts its discharge frequency to inc ...
.
In bluntnose knifefishes, ''
Brachyhypopomus
''Brachyhypopomus'' is a genus of fish in the family Hypopomidae (bluntnose knifefish) native primarily to tropical and subtropical South America (south to the Río de la Plata Basin), although a single species, ''B. occidentalis'', also occurs ...
'', the electric discharge pattern is similar to the low voltage electrolocative discharge of the
electric eel
The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
, ''Electrophorus''. This is hypothesized to be
Batesian mimicry
Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on bu ...
of the powerfully-protected electric eel.
''Brachyhypopomus'' males produce a continuous electric "hum" to attract females; this consumes 11–22% of their total energy budget, whereas female electrocommunication consumes only 3%. Large males produced signals of larger amplitude, and these are preferred by the females. The cost to males is reduced by a
circadian rhythm
A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...
, with more activity coinciding with night-time courtship and spawning, and less at other times.
Fish that prey on electrolocating fish may "eavesdrop"
on the discharges of their prey to detect them. The electroreceptive
African sharptooth catfish
''Clarias gariepinus'' or African sharptooth catfish is a species of catfish of the family Clariidae, the airbreathing catfishes.
Distribution
They are found throughout Africa and the Middle East, and live in freshwater lakes, rivers, and sw ...
(''Clarias gariepinus'') may hunt the weakly electric mormyrid, ''
Marcusenius
''Marcusenius'' is a genus of elephantfishes native to Africa. Its members are highly diverse in size, with the smallest species reaching less than and the largest more than .
The genus is named after Johann Marcusen.
Species
There are cur ...
macrolepidotus'' in this way. This has driven the prey, in an
evolutionary arms race
In evolutionary biology, an evolutionary arms race is an ongoing struggle between competing sets of co-evolving genes, phenotypic and behavioral traits that develop escalating adaptations and counter-adaptations against each other, resembling an a ...
, to develop more complex or higher frequency signals that are harder to detect.
Some shark embryos and pups "freeze" when they detect the characteristic electric signal of their predators.
Evolution and taxonomic distribution
In
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s, passive electroreception is an
ancestral trait, meaning that it was present in their last common ancestor.
The ancestral mechanism is called ampullary electroreception, from the name of the receptive organs involved,
ampullae of Lorenzini. These evolved from the mechanical sensors of the
lateral line, and exist in
cartilaginous fishes (
shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...
s,
rays
Ray may refer to:
Fish
* Ray (fish), any cartilaginous fish of the superorder Batoidea
* Ray (fish fin anatomy), a bony or horny spine on a fin
Science and mathematics
* Ray (geometry), half of a line proceeding from an initial point
* Ray (gra ...
, and
chimaeras),
lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
es,
bichir
Bichirs and the reedfish comprise Polypteridae , a family of archaic ray-finned fishes and the only family in the order Polypteriformes .Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The Diversity of Fishes. West Sussex, UK: Blackwell Pu ...
s,
coelacanth
The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...
s,
sturgeon
Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...
s,
paddlefish
Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elongla ...
es, aquatic
salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s, and
caecilian
Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
s. Ampullae of Lorenzini appear to have been lost early in the
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of bony fishes and
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s, though the evidence for absence in many groups is incomplete and unsatisfactory.
Where electroreception does occur in these groups, it has secondarily been acquired in evolution, using organs other than and not
homologous with ampullae of Lorenzini.
Electric organs have evolved at least eight separate times, each one forming a
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
: twice during the evolution of cartilaginous fishes, creating the electric skates and rays, and six times during the evolution of the bony fishes.
Passively-electrolocating groups, including those that move their heads to direct their electroreceptors, are shown without symbols. Non-electrolocating species are not shown.
Actively electrolocating fish are marked with a small yellow lightning flash
![Farm-Fresh lightning](https://upload.wikimedia.org/wikipedia/commons/5/59/Farm-Fresh_lightning.png)
and their characteristic discharge waveforms.
Fish able to deliver electric shocks are marked with a red lightning flash
![Lightning Symbol](https://upload.wikimedia.org/wikipedia/commons/c/c7/Lightning_Symbol.svg)
.
Cartilaginous fish
Sharks and rays (''
Elasmobranchii
Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of ...
'') 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. Sharks are the most electrically sensitive animals known, responding to
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
fields as low as 5 nV/cm.
Bony fish
Two groups of
teleost
Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
fishes are weakly electric and actively electroreceptive: the Neotropical knifefishes (
Gymnotiformes) and the African elephantfishes (
Notopteroidei
Notopteroidei is a suborder of the order Osteoglossiformes that contains the extant families Gymnarchidae (aba), Notopteridae (feather backs and knifefish) and Mormyridae
The Mormyridae, sometimes called "elephantfish" (more properly freshwat ...
), enabling them to navigate and find food in turbid water.
The Gymnotiformes include the
electric eel
The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
, which besides the group's use of low-voltage electrolocation, is able to generate high voltage electric shocks to stun its prey. Such powerful electrogenesis makes use of large
electric organs modified from muscles. These consist of a stack of electrocytes, each capable of generating a small voltage; the voltages are effectively added together (
in series) to provide a powerful electric organ discharge.
Monotremes
![Platypus electrolocation](https://upload.wikimedia.org/wikipedia/commons/e/e4/Platypus_electrolocation.svg)
The
monotremes, including the semi-aquatic
platypus
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...
and the terrestrial echidnas, are the only group of mammals that have evolved electroreception. While the electroreceptors in fish and
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves. The electroreceptors of monotremes consist of free nerve endings located in the
mucous gland
Mucous gland, also known as muciparous glands, are found in several different parts of the body, and they typically stain lighter than serous glands during standard histological preparation. Most are multicellular, but goblet cells are single-cel ...
s of the
snout. Among the monotremes, the
platypus
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...
(''Ornithorhynchus anatinus'') has the most acute electric sense.
The platypus localises its prey using almost 40,000 electroreceptors arranged in front-to-back stripes along the bill.
The arrangement is highly directional, being most sensitive off to the sides and below. By making short quick head movements called
saccade
A saccade ( , French for ''jerk'') is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishi ...
s, platypuses accurately locate their prey. The platypus appears to use electroreception along with
pressure sensors
A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually act ...
to determine the distance to prey from the delay between the arrival of electrical signals and pressure changes in water.
The electroreceptive capabilities of the four species of
echidna
Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...
are much simpler.
Long-beaked echidna
The long-beaked echidnas (genus ''Zaglossus'') make up one of the two extant genera of echidnas, spiny monotremes that live in New Guinea; the other being the short-beaked echidna. There are three living species and one extinct species in this ge ...
s (genus ''Zaglossus'') have some 2,000 receptors, while
short-beaked echidna
The short-beaked echidna (''Tachyglossus aculeatus''), also called the short-nosed echidna, is one of four living species of echidna and the only member of the genus ''Tachyglossus''. It is covered in fur and spines and has a distinctive snou ...
s (''Tachyglossus aculeatus'') have around 400, near the end of the snout.
This difference can be attributed to their habitat and feeding methods.
Western long-beaked echidna
The western long-beaked echidna (''Zaglossus bruijnii'') is one of the four extant echidnas and one of three species of '' Zaglossus'' that occurs in New Guinea. Originally described as ''Tachyglossus bruijnii'', this is the type species of ''Zag ...
s feed on
earthworms
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...
in leaf litter in tropical forests, wet enough to conduct electrical signals well. Short-beaked echidnas feeds mainly on
termite
Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatto ...
s and
ant
Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...
s, which live in nests in dry areas; the nest interiors are presumably humid enough for electroreception to work.
Experiments have shown that
echidna
Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...
s can be trained to respond to weak electric fields in water and moist soil. The electric sense of the echidna is hypothesised to be an evolutionary remnant from a platypus-like ancestor.
Dolphins
Dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s have evolved electroreception in structures different from those of fish,
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s and
monotremes. The hairless
vibrissal crypts on the
rostrum
Rostrum may refer to:
* Any kind of a platform for a speaker:
**dais
**pulpit
* Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects
* Rostrum (ship), a form of bow on naval ships
* Ros ...
of the
Guiana dolphin
The Guiana dolphin (''Sotalia guianensis''), also known as the estuarine dolphin or costero, is a dolphin found in the coastal waters to the north and east of South America, and east of Central America. It is a member of the oceanic dolphin fami ...
(''Sotalia guianensis''), originally associated with mammalian whiskers, are capable of electroreception as low as 4.8 μV/cm, sufficient to detect small fish. This is comparable to the sensitivity of electroreceptors in the platypus.
Bees
Until recently, electroreception was known only in
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s. Recent research has shown that
bees can detect the presence and pattern of a static charge on flowers.
See also
*
Active sensory systems
Active sensory systems are sensory receptors that are activated by probing the environment with self-generated energy. Examples include echolocation of bats and dolphins and insect antennae. Using self-generated energy allows more control over sig ...
*
Feature detection (nervous system) Feature detection is a process by which the nervous system sorts or filters complex natural stimuli in order to extract behaviorally relevant cues that have a high probability of being associated with important objects or organisms in their environ ...
*
Magnetoreception
Magnetoreception is a sense which allows an organism to detect the Earth's magnetic field. Animals with this sense include some arthropods, molluscs, and vertebrates (fish, amphibians, reptiles, birds, and mammals, though not humans). The se ...
References
Further reading
*
External links
ReefQuest Centre for Shark ResearchElectrolocation on Scholarpedia
{{Sensation and perception
Electroreceptive animals
Ethology
Ichthyology
Perception
Physiology
Sensory systems