Electroreception

Electroreception or electroception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, because water is a much better conductor than air. The known exceptions are the monotremes(echidnas and platypuses), cockroaches and bees. Electroreception is used in electrolocation (detecting objects) and for electrocommunication. Electroreception or electroception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, because water is a much better conductor than air. The known exceptions are the monotremes(echidnas and platypuses), cockroaches and bees. Electroreception is used in electrolocation (detecting objects) and for electrocommunication. Until recently, electroreception was known only in vertebrates. Recent research has shown that bees can detect the presence and pattern of a static charge on flowers. In vertebrates, electroreception is an ancestral trait, that is to say that it was present in the last common ancestor of all vertebrates.. This form of ancestral electroreception is called ampullary electroreception, with the receptive organs themselves called Ampullae of Lorenzini. Not all vertebrates that possess electroreception have Ampullae of Lorenzini. Ampullae of Lorenzini exist in cartilaginous fishes (sharks, rays, chimaeras), lungfishes, bichirs, coelacanths, sturgeons, paddlefish, aquatic salamanders, and caecilians. Other vertebrates that have electroreception such as catfish, gymnotiformes, Mormyridiformes, monotremes, and at least one species of cetacean all have different secondarily derived forms of electroreception. Ampullary electroreception is passive, and is used predominantly in predation. Two groups of teleost fishes are weakly electric and engage in active electroreception: the Neotropical knifefishes (Gymnotiformes) and the African elephantfishes (Notopteroidei). A rare terrestrial exception is the Western long-beaked echidna which has about 2,000 electroreceptors on its bill, compared to 40,000 for its semi-aquatic monotreme relative, the duck-billed platypus. Electroreceptive animals use this sense to locate objects around them. This is important in ecological niches where the animal cannot depend on vision: for example in caves, in murky water and at night. Many fish use electric fields to detect buried prey. Some shark embryos and pups 'freeze' when they detect the characteristic electric signal of their predators. It has been proposed that sharks can use their acute electric sense to detect the earth's magnetic field by detecting the weak electric currents induced by their swimming or by the flow of ocean currents. The walking behaviour of cockroaches can be affected by the presence of a static electric field: they like to avoid the electric field. Cabbage loopers are also known to avoid electric fields. In active electrolocation, the animal senses its surrounding environment by generating electric fields and detecting distortions in these fields using electroreceptor organs. This electric field is generated by means of a specialised electric organ consisting of modified muscle or nerves. This field may be modulated so that its frequency and wave form are unique to the species and sometimes, the individual (see Jamming avoidance response). Animals that use active electroreception include the weakly electric fish, which either generate small electrical pulses (termed 'pulse-type') or produce a quasi-sinusoidal discharge from the electric organ (termed 'wave-type'). These fish create a potential which is usually smaller than one volt. Weakly electric fish can discriminate between objects with different resistance and capacitance values, which may help in identifying the object. 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. 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 pumps associated with osmoregulation at the gill membrane. This field is modulated by the opening and closing of the mouth and gill slits. Many fish that prey on electrogenic fish use the discharges of their prey to detect them. This has driven the prey to evolve more complex or higher frequency signals that are harder to detect. Passive electroreception is carried out solely by ampullary electroreceptors in fish. It is tuned to low frequency signals (below one up to tens of Hertz). Fish use passive electroreception to supplement or replace their other senses when detecting prey and predators. In sharks, sensing an electric dipole alone is sufficient to cause them to try to eat it. Weakly electric fish can also communicate by modulating the electrical waveform they generate, an ability known as electrocommunication.They may use this for mate attraction and territorial displays. Some species of catfish use their electric discharges only in agonistic displays. In one species of Brachyhypopomus (a genus of South American river fish belonging to the family Hypopomidae, commonly known as bluntnose knifefishes), the electric discharge pattern is similar to the low voltage electrolocative discharge of the electric eel. This is hypothesised to be a form of Batesian mimicry of the powerfully-protected electric eel.