Electrical orientation
Electrical orientation (also: electroreception or electrical sensors ) describes the ability of some living beings to perceive an electrical field via special receptors . This is also known as passive electrical orientation .
Some living beings from different realms can use electrical organs to generate weak or strong electrical charges and release them to their environment ( Electric Organ Discharge , EOD ). For orientation purposes, electrical fields are then generated and received (transmitter-receiver combination). This is known as active electrical orientation . In addition, the actively generated electricity can be used for hunting, defense or intra-species communication.
Both salt and fresh water conduct electricity due to the released mobile charge carriers ( ions ). Because of the particularly good electrical conductivity of salt water, fish with an active electrical orientation predominantly appear in fresh water, as they could otherwise injure themselves.
Groups of living things
Some species in different groups of living things are capable of electrical orientation, but closely related species may not be able to do so. The following animal species have been examined, they are representative of species not mentioned, but do not allow any statements about the qualifications of related species.
Microorganisms
A number of microorganisms such as Schizosaccharomyces pombe have been shown to align themselves with the electric field.
Flowering plants
Many flowering plants are capable of active electrical orientation. A lot of pollen carries static charges, so the plant can register the arrival of pollen (from insects ) in the flower and improve the opening of the flower. The electrical field it creates can change the plant within seconds to respond to incoming pollen or insects. This phenomenon is used for industrial electrostatic dusting .
insects
For insects visiting flowers such as the honey bee or the dark bumblebee and many other insects, the ability of electrical reception has been proven. The electrical field generated by the plant guides the insect, like the scent or the visually effective colors, to the flower. Bumblebees , fruit flies , blowflies and other insects actively influence the electrical field because they carry static electrical charges.
Round mouths
Lampreys have a passive electrical orientation and presumably the common ancestors of vertebrates , round mouths and jaw mouths , had a corresponding sensory organ.
Cartilaginous fish
The passive electrical sense of direction is present in many sharks and rays within the class of cartilaginous fish .
Active electrical orientation also exists within the family of the real rays (Rajidae).
A very well-studied example within the family of the torpedo is the marbled electric ray Torpedo marmorata .
Bony fish
Many bony fish have the ability for passive electrical orientation and can use their electroreceptors to detect prey, enemies and the earth's magnetic field . So far, electrical sense has been developed in the South American lungfish , various sturgeon species (e.g. spoonbill & the shovel sturgeon ), in the pike -fish , many catfish-like (probably all are electro-receptive) and the African species of the old world knife fish ( African flag knife fish and African Knife fish ), but not with the Asian ones. In bony fish, the active electrical orientation is of minor importance. The electroreceptors developed from the lateral line organ , which lost its original function. Electrical organs, however, have developed three to four times independently of one another in soil forms and residents of cloudy and poor-light waters. A total of nine families from four orders have electrical organs, among the catfish the trembling catfish , all five families of the New World knife fish (Gymnotiformes), the Nilhechte and the Greater Nilhecht from the order of the bone-flickering and the electric stargazers ( Astroscopus ) (family Himmelsgucker (Uranoscopidae) , the only perch relatives with electrical organs), together approx. 400 species.
Mammals
The passive electrical sense of direction can also be found in platypus .
The Guyana dolphin , also found in rivers, has a passive electrical sense of direction.
organs
Electroreceptors
In order to recognize electrical currents or changes in self-generated electrical fields, there are special pores in the fish's skin, at the base of which are the electroreceptors. These receptors differ from one another in that they sense different aspects of electric fields. In addition, some are tailored to their own discharges, others to those of conspecifics or related species.
The electroreceptors do not have their own axons and are therefore secondary sensory cells. They are derived from hair sensory cells and are innervated by branches of the statoacusticus nerve.
There are two types of electroreceptors morphologically: ampullary receptors and tuberous receptors. They differ mainly in that the ampullary receptors such. B. the Lorenzini ampoules in sharks are open to the outside. In contrast, the tuberous receptors are not open to the outside and are therefore less sensitive.
The apical membrane of the receptor cells has a low electrical resistance. An electrical impulse can pass through the membrane through the receptor cells and depolarize the basal receptor cell membrane. This triggers the influx of calcium ions, which in turn releases transmitters . The transmitter molecules post-synaptically influence the discharge frequency of the afferent nerve fibers, the terminals of which are attached to the basal receptor membrane. The respective increase or decrease of the discharge frequency depends on how strongly the electric field that the fish has emitted is influenced, or what type of electrical impulses arrive.
Lorenzini ampoules
Lorenzini ampoules are the electroreceptors of the cartilaginous fish and are used for passive orientation. You can sense geomagnetic fields, electrical fields created by animals through muscle activity, and large ocean currents.
Lorenzini ampoules are tubular ampoule organs that are derived from the lateral line organs. One end of the ampoule is tubularly open to the external medium, and the other end forms a closed, spherical chamber. The tube is filled with an electrically very conductive gelatinous substance ( mucus ) , which also serves to protect the electroreceptors from the outside water, whereas the tube wall has a high electrical resistance. That makes the tube a very good electrical conductor. The tube connects the apical membrane of the electroreceptors, up to a hundred of which are in the chamber wall, through the gelatinous substance with the external medium.
The Lorenzini ampoule is a highly sensitive DC voltmeter. A constant quiescent current flows through the receptors, triggering tonic impulses. The individual receptors are ion-tightly linked to their neighboring cells, so that current can only flow through their apical membrane. If the electric field of the fish changes, the resting discharge frequency changes up or down (depending on the direction of the current flowing).
The fact that the individual inputs of the ampoule organs are connected convergently means that greater sensitivity can be achieved at the receptor level (see central nervous processing). With the Lorenzini ampoules, sharks can perceive electric fields that are only 0.01 to 0.05 microvolts per centimeter.
- Significance of the Lorenzini ampoules using the example of the sharks
In sharks , the Lorenzini ampoules are on the head and snout and are visible as small, dark pore openings. Due to their properties, the ampoules are used for electrical location. Living organisms inevitably create an electrical voltage through muscle activity that is even noticeable when buried under sand. However, such a location can only take place within a very small radius. The Lorenzini ampoules are used to locate the prey at the last moment of the attack or to search for buried creatures on the ground.
The ampoules also serve as a “geomagnetic compass”, as ocean currents inevitably produce electrical magnetic fields that the shark can feel. Thus, for example, the sharks can gather to mate at a specific time and place.
According to some findings, the Lorenzini ampoules are also used for thermal reception. Cooling increases the discharge rate, whereas warming briefly lowers the frequency of the action potentials .
Tubular organs
In order to perceive the change in the specially emitted electric fields, the New World knifefish (Gymnotiformes) have tubular organs that are tuned to their high-frequency electrical discharges. Similar to the Lorenzini ampoules, these are sunk into the skin, but capacitively coupled to the external medium (water) by cover cells. Thus, high-frequency alternating fields can be perceived. Since the organ is shielded at the edge with "tight junctions", the cover cells act like a lens that directs the voltage gradient directly to the receptor cells. These receptor cells lie on the tubule base and about 95% of their membrane surface is exposed to the tubule interior. The stimulus threshold of the receptor cells is always at the animal's own discharge frequency, although the method of coordination cannot yet be explained.
There are two types of tubular receptors. On the one hand, there are the P receptors, which are sensitive to small changes in the amplitude of the electric field. They are connected to both effector and inhibitory neurons, with an increase or decrease in amplitude leading either to excitation or to inhibition. As with lateral inhibition in the vertebrate retina, (electrical) contrasts can be intensified and weak field changes can be better perceived. The P receptors quickly adapt to electrical stimuli.
The second type of receptor are the T-units. They are time encoders that send out a single spike each time an electric field crosses the zero line between positive and negative. There is no adaptation for the T-units.
With the two types of receptors, the gymnotids can not only differentiate between ohmic and capacitive resistances in their electrical field, but also analyze interferences with alternating electrical fields from other electrical fish.
Mormyromasts and tuberous organs
The tuberous organs of the Nilhechte (Mormyridae) are time coders that function like the T-units of the New World knife fish. They also send single spikes when crossing the zero line of the electric field. The tuber organs are used to communicate with other fish.
The Mormyromasts are constructed similarly to the tubular organs of the New World Knifefish, but more differentiated. They have A receptors that are embedded in the chamber wall and only exposed to the surrounding water through the apical membrane. The A receptors are amplitude encoders. In addition, there are B-receptors in an inner chamber below the main chamber, each of which is completely surrounded by the outside water (100% of the membrane surface). These are capacitively coupled to the water and react very sensitively to changes in the waveforms of the electric field. They are time coders. The Mormyromasts are used for electrical localization.
Active electrical organs
Electroplax
Electrical discharges are generated in electrical organs called electroplaxes. The electroplax is made up of electrocytes , which are connected to form columns as electrical plates. The electrocytes are mainly formed from tail, trunk and neck muscle cells and consist of modified muscle fibers that no longer contain myofibrils and are therefore incapable of contraction. Each electrocyte is created by the fusion of several muscle fibers, which explains why the electrocytes are significantly larger than muscle fibers. In the trembling catfish , the electrocytes are 20–40 μm thick and approx. 1 mm long. Several electrical organs can occur per individual: the electric eel, for example, has three organs that generate particularly strong impulses when they are discharged together.
One side of what is known as an electrical plate is smooth and resembles a neuromuscular end plate. It is connected (innervated) to motor spinal nerves. These have a very high synapse density . The generation of electricity in the individual electrocytes is based on the membrane potential difference between the two sides of the electrical plate.
The other side is papillary and has many capillaries that serve to supply the electrical cells with oxygen and nutrients, as the electrical discharges consume a lot of energy. Due to the high density of synapses on the smooth side and many acetylcholine receptors in their postsynaptic membranes, a lightning-like inversion (reversal) of the membrane potential on this side is possible. This is done with great precision and synchronously. There are also special neurons of various thickness and length that are used for synchronization (see 3.b.iii).
By reversing the membrane potential of the innervated side, there is a potential difference of up to 140 mV between the two sides of the electrocyte. So that such a voltage can be built up between the two sides of the cell and it functions as a kind of “battery”, both sides are isolated from one another in a way that has not yet been known. Since these 140 mV represent a barely perceptible voltage, larger voltages are generated through a series (one behind the other) arrangement of many thousands of electrical plates. The voltage contributions of the individual plates add up and can amount to several hundred to almost a thousand volts.
Higher currents are achieved by arranging the electrical plates in parallel (next to one another). This is why electrical organs in fish are either large-area or drum-shaped. Either a larger current or voltage can be generated.
The electrical organs can be located in different parts of the body of the fish and can assume different sizes, which is related to the function of the electrical discharges, among other things. In the electric eel , almost all of the trunk muscles are used to generate electricity, whereas in the stargazer only one of the six eye muscles becomes an electrical organ.
A distinction is made between strong and weak electric fish. The strongly electric fish (trembling fish) use their bioelectricity as a weapon, the weakly electric fish ( knife eels , Nile pike - see active electrolocation) emit electric signals for orientation and communication.
When discharged, the fish becomes a dipole , with either the head or tail end being the plus pole. This depends on the location of the innervated membrane of the electroplaxis. The discharge can be either monophasic or biphasic. This depends on the membrane properties of the papillary (non-innervated) membrane: If this cannot be excited chemically or electrically, the discharge is monophasic. If, on the other hand, it is excitable, the discharge is biphasic. The discharge of the innervated membrane section is followed by the discharge of the non-innervated membrane section. The discharge thus receives two peaks (plus and minus), which can be observed especially in weakly electric fish.
Signal processing
Central nervous processing
The electroreceptors are innervated by neurons of the peripheral collateral organ. The individual receptor cells are connected convergently in order to increase the electrical sensitivity. Nevertheless, the different types of receptors (time and amplitude coding) remain separate until they are differentially interconnected in the midbrain. So the point in time of the zero crossings and the increase or decrease in amplitude.
In the ELL (electrosensory lateral line lobe), into which the electroreceptors project, the signals from the various receptors arrive in parallel and a topographical image of the electrosensitive skin takes place. The contrasts are increased by antagonistic fields.
The time coding at different areas of the skin is compared and it is determined how the phase of the disturbed electric field shifts. Local changes are thus precisely differentiated. In addition, this “electrical image” is “superimposed” on the visual image in the fish's brain (tectum opticum), thus completing it.
Neural feedback
A distinction is made between negative and positive feedback. The negative feedback occurs through antagonistic excitation by the cells of the granular layer (via the parallel fibers) and ensures that the electroreceptors do not react to their own electrical discharges and that an adaptation takes place at repetitive frequencies. This keeps the receptor capacity free for singular (new = important) signals. Positive feedback is about increasing the local electrical excitation and electrical contrasts. This is very important for electrolocation.
Active electrical location functions
Electric fields
The electric field spreads around the dipole (fish) from head to tail tip (graphic). Objects that are in the fish's electric field produce an amplitude and phase shift in its electric field, as their electrical conductivity differs from that of water.
Lower electrical resistance than water (capacitive) leads to a compression of the local electrical field lines. Higher electrical resistance (resistive, ohmic) leads to a thinning.
However, the range of the electrolocation is limited to a very small radius, which corresponds to about half the length of the fish. The modulations of the electric field by objects are very small and the fish have to swim past them directly and several times; however, the electrical images are just blurry.
The distance to an object is determined by the maximum amplitude and the sharpness of contrast. Objects that are further away have a lower maximum amplitude and are more “blurred” (indistinct electrical contrasts). On the basis of the capacitive resistances, the animals can differentiate between animate and inanimate objects.
The Mormyrids with their Mormyromasts perceive differences in the signals of the A and B receptors and can thus differentiate between resistive and capacitive objects: With resistive objects, both signals cancel each other, with capacitive objects there is a strong difference between the signals from A and B. Receptors. However, the higher the conductivity of the water, the lower the sensitivity of the electrolocation, as the amplitude of the fish's electric field decreases at the same time. The modulation of the amplitudes must be "amplified" through positive neural feedback. In addition, the amplitude modulation is very low even under optimal conditions. For this reason, the electrolocation is mostly used as an additional aid in combination with the sense of smell, when the optical sense organs can no longer provide sufficient information (night / cloudy waters). So one can assume that the communicative function of the electrical discharges is biologically more important than the location.
orientation
For active electrical orientation, the fish itself sends out an electrical field and perceives its change through receptors. Active electrical localization is advantageous if, for example, the lateral direction of the fish does not provide sufficient orientation, for example in very fast and turbulent flowing waters, or where visual perception is difficult (cloudy waters, darkness). However, active electrical location is limited to a small area. The strength of the electric field decreases with the fourth power of the distance and the detection rate decreases with the square of the distance.
There are two different large groups of weakly electric fish that actively orient themselves electrically. On the one hand there are the gymnotids ( knife eels ), South American freshwater fish, which can generate sinusoidal electrical discharges. This requires a large number of electrical cells to be excited at the same time. They have tubular organs with which they register the change in their self-generated electrical fields. On the other hand, there are the Mormyrids , African freshwater fish, which generate pulse-shaped electrical discharges, which can be mono-, bi- or triphasic. Up to 100 discharges per second are possible.
Due to the sometimes very high discharge frequency, the neural connection from the medulla oblongata , the elongated medulla, to the electroplaxis is synchronized by axon stems of different lengths and thicknesses . This synchronization is based on the principle of electrical resistance. The thicker "lines" have a lower electrical resistance and run directly to the more distant electroplaxes. The thinner ones conduct electrical impulses more slowly and take a “detour” to the closer electrical cells.
The Mormyrids have tuberous organs and Mormyromasts for electrical reception.
communication
Because the change in phases, amplitudes (tubular, Mormyromast, tuberous organs) and direct voltage potential (ampoules) is measured in parallel and these are amplified and combined neuronally, the animals can differentiate between conspecifics and alien ones, as well as sexual partners. This distinction is made on the basis of the form of discharge and the repetition rate, since the basic type is specific to the species and gender and the amplitude in connection with the length of the pauses enables individual recognition.
From the fact that dominant animals have a higher discharge frequency, one can see that social interaction also takes place in this way.
For courtship and in cases of aggression, the males chop up their continuous discharges into short bursts (chirps). These chirps serve as a necessary key stimulus for females to spawn. However, an increase in the transmission frequency indicates aggression.
However, the radius of electrical communication is a maximum of one meter.
Bioelectricity as a weapon
Strongly electric fish are known as tremors. Tremor fish do not usually have any tuberous electroreceptors, but they belong to the electric fish class and should therefore be mentioned for the sake of completeness.
A particular example is the electric eel . Its entire tail muscle (approx. 70% of the body) has been converted to generate electricity. Due to this size, up to 6000 electrocytes are connected in series and in parallel, which leads to high voltages. Adult specimens can generate voltages of at least 600 volts for about two milliseconds with the Elektroplax , the largest ones up to 860 volts and 1 ampere current, which corresponds to a short-term output of 860 watts. The electric eel can emit both strong and weak electrical discharges, which are used on the one hand to catch prey, on the other hand to delimit the territory and to find reproductive partners. The eel acts as an electrical dipole with the positive pole on the head and the negative pole on the tip of the tail.
The animals are protected from electric shocks by themselves or other individuals by the insulating skin or additional layers of fat around vital organs.
Electric rays can deliver electrical discharges of 60 to 230 V and over 30 A to paralyze their victims. In the case of the spotted electric ray , the current strength can reach 50 A, whereby this extremely high value was proven with a voltage of 'only' 60 V.
swell
- TH Bullock, CD Hopkins, AN Popper, RR Fay: Electroreception. Springer Handbook of Auditory Research. Springer Verlag, Berlin 2005, ISBN 0-387-23192-7 .
- R. Eckert: Animal Physiology . Thieme Verlag, Stuttgart 2002.
- W. Heiligenberg: Neural nets in electric fish . MIT Press, Cambridge, MA 1991.
- G. Heldmaier, G. Neuweiler: Comparative animal physiology . 1st volume, Springer Verlag, Berlin 2003.
Secondary literature
- RW Turner, L. Maler, M. Burrows: Electroreception and electrocommunication. In: J Exp Biol. Vol. 202, 1999, pp. 1167-1458.
- G. von der Emde: Electroreception. In: DH Evans (Ed.): The Physiology of Fishes. 2nd Edition. CRC Press, Boca Raton (Florida) 1998, pp. 313-343.
Individual evidence
- ↑ Günther Sterba : Freshwater fish of the world. 2nd Edition. Urania, Leipzig / Jena / Berlin 1990, ISBN 3-332-00109-4 .
- ↑ Gerard H. Markx, Burçak Alp, Alastair McGilchrist: Electro-orientation of Schizosaccharomyces pombe in high conductivity media. In: Journal of Microbiological Methods. 50, No. 1, 2002, pp. 55-62, doi: 10.1016 / S0167-7012 (02) 00012-X .
- ↑ a b Y. Dai, SE Law: Modeling the transient electric field produced by a charged pollen cloud entering a flower. In: Industry Applications Conference, 1995. Thirtieth IAS Annual Meeting, IAS '95., Conference Record of the 1995 IEEE.
- ^ Yiftach Vaknin, S. Gan-Mor, A. Bechar, B. Ronen, D. Eisikowitch: The role of electrostatic forces in pollination. In: Plant Systematics and Evolution. 222, Vol. 1-4, 2000, pp. 133-142.
- ^ Yiftach Vaknin, Samuel Gan-mor, Avital Bechar, Beni Ronen, Dan Eisikowitch: Are flowers morphologically adapted to take advantage of electrostatic forces in pollination? In: New Phytologist. 152, No. 2, 2001, pp. 301-306, doi: 10.1046 / j.0028-646X.2001.00263.x .
- ↑ a b Dominic Clarke: Detection and learning of floral electric fields by bumblebees. In: Science . Online advance publication of February 21, 2013, doi: 10.1126 / science.1230883
- ^ S. Edward Law: Agricultural electrostatic spray application: a review of significant research and development during the 20th century. In: Journal of Electrostatics. 51, 2001, pp. 25-42, doi: 10.1016 / S0304-3886 (01) 00040-7 .
- ^ Daniel Robert et al: News and events. In: Eur J Ophthalmol. 10, No. 2, 2000, pp. 132-136.
- ↑ a b Victor Manuel Ortega-Jimenez, Robert Dudley: Spiderweb deformation induced by electrostatically charged insects. In: Scientific Reports. 3, no.2108 , July 2013, doi: 10.1038 / srep02108 .
- ↑ David Bodznick, R. Glenn Northcutt: Electro Reception in lampreys: evidence did the earliest vertebrates were electro receptive. In: Science 212, No. 4493, 1981, pp. 465-467.
- ↑ Ad J. Kalmijn: Electro-orientation in sharks and rays: theory and experimental evidence. (PDF) No. SIO-Ref-73-39. SCRIPPS Institution of Oceanography La Jolla California, November 1973.
- ↑ Marcelo Camperi et al .: From morphology to neural information: The electric sense of the skate. In: PLOS Computational Biology. Volume 3, 2007, pp. 1083-1096, e113. doi: 10.1371 / journal.pcbi.0030113 .
- ↑ Wilfried Westheide, Gunde Rieger: Special Zoology. Part 2: vertebrates or skulls . Springer-Verlag, 2014, ISBN 978-3-642-55436-0 , pp. 224 ( limited preview in Google Book Search [accessed December 15, 2017]).
- ↑ Kurt Fiedler: Textbook of Special Zoology, Volume II, Part 2: Fish . Gustav Fischer Verlag Jena 1991, ISBN 3-334-00339-6 , pp. 112-119.
- ^ Nicole U. Czech-Damal et al .: Electroreception in the Guiana dolphin (Sotalia guianensis) . In: Proceedings of the Royal Society B . Volume 279, No. 1729, 2011, pp. 663-668, doi: 10.1098 / rspb.2011.1127
- ↑ GN Akoev, NO Vol'pe: Analysis of the mechanism of perception of temperature stimuli by the ampullae of Lorenzini of Black Sea skates. In: Fiziol Zh SSSR Im IM Sechenova. Volume 64, 1978, pp. 1681-1688.
- ↑ GA Unguez, HH Zakon: Phenotypic conversion of distinct muscle fiber populations to electrocytes in a weakly electric fish. In: J Comp Neurol. Volume 399, 1998, pp. 20-34. PMID 9725698
- ↑ T. Schikorski: Functional neuroanatomy of the electromotive system of the trembling catfish Malapterurus electricus . Dissertation . Department of Biology at the Johann Wolfgang Goethe University, Frankfurt am Main 1993, DNB 94312669X .
- ↑ Amazon Shocker Facts . In: Nat Geo WILD . June 6, 2014 ( nationalgeographic.com [accessed December 9, 2016]).
- ↑ Monster Eel, Monster Shock? (No longer available online.) In: Nat Geo TV Blogs. July 21, 2014, archived from the original on December 10, 2016 ; Retrieved December 9, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ How do electric eels generate a voltage and why do they not get shocked in the process? In: Scientific American . ( scientificamerican.com [accessed December 9, 2016]).
- ↑ Kathrin Passig, Aleks Scholz, Kai Schreiber: The new lexicon of ignorance: What there has been no answer so far . Rowohlt E-Book, 2011, ISBN 978-3-644-11011-3 ( limited preview in Google Book Search [accessed May 6, 2016]).
