electroreceptor

Electroreception, sometimes called electroception, is the biological ability to perceive electrical impulses. It is particularly common among aquatic creatures since salt water is a much more efficient conductor than air. It is used for electrolocation (detecting objects) and for electrocommunication. There are no known cases of mimicry involving electroreception, though it is theoretically possible.^[1]

Overview

Active electrolocation. Conductive objects concentrate the field and resistant objects spread the field.

Electroreception is found in lampreys, cartilaginous fishes (sharks, rays, and chimaeras), lungfishes, bichirs, coelacanths, sturgeons, paddlefishes, catfishes, Neotropical knifefishes, and elephantfishes. The electroreceptors are believed to be derived from the lateral line. In most of these groups, electroreception is passive, while the weakly electric knifefishes and elephantfishes engage in active electroreception.

Passive

In passive electroreception the animal senses the weak bioelectric fields generated by other animals.

Active

In active electroreception, the animal senses its surrounding environment by generating electric fields and detecting distortions in these fields using electroreceptor organs. Active electrolocation is especially important in murky water, where visibility is low.

Animals that use active electroreception include the weakly electric fish, which generate small (typically less than one volt) electrical pulses using an organ in the tail consisting of two to five rows of modified muscle cells (electrocytes).

Weakly electric fish can discriminate between objects with different resistance and capacitance values, which may help in identifying the object. They can also communicate by modulating the electrical waveform they generate; an ability known as electrocommunication.^[2]

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

Sensory Mechanism

Active electroreception relies upon tuberous electrororeceptors which are sensitive to high frequency (20-20,000 Hz) stimuli. These receptors have a loose plug of epithelial cells which capacitively couples the sensory receptor cells to the external environment. Passive electroreception however, relies upon ampullary receptors 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. Mormyrid electric fish from Africa use tuberous receptors known as Knollenorgans to sense electric communication signals.

Occurrence

Elasmobranchii

Electroreceptors (Ampullae of Lorenzini) and lateral line canals in the head of a shark.

Sharks and rays (members of the subclass Elasmobranchii) rely heavily on electrolocation 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 DC fields as low as 5 nV/cm.

The electric field sensors of sharks are called the ampullae of Lorenzini. They consist of electroreceptor cells connected to the seawater by pores on their snouts and other zones of the head. A problem with the early submarine telegraph cables was the damage caused by sharks who sensed the electric fields produced by these cables. It is possible that sharks may use Earth's magnetic field to navigate the oceans using this sense.

A recent study has suggested that the same genes that contribute to a shark's sense of electroreception may also be responsible at least in part to the development of facial structures in humans.^[3]

Other vertebrates

The Platypus also uses electroreception.

The electric eel, besides its ability to generate high voltage electric shocks, uses lower voltage pulses for navigation and prey detection in its turbid habitat. This ability is shared with other Gymnotiformes.

Monotremes are the most prevalent mammals that use electroception. Among these, the platypus has the most acute sense.^[4][5] The platypus appears to use electroreception along with pressure sensors to determine the distance to prey from the delay between the arrival of electrical signals and pressure changes in the water.^[5]

See also

• Bioelectromagnetism

References

External links

• ReefQuest Centre for Shark Research
• "Sharks' Sixth Sense Related to Human Genes", LiveScience, February 7, 2006.
• "Geeky Rare-Earth Magnets Repel Sharks", Wired, May 15, 2007.
• Electrolocation on Scholarpedia