Locomotor and electric displays associated with electrolocation during exploratory behavior in mormyrid fish (original) (raw)
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Philosophical Transactions of the Royal Society B, 2000
Weakly electric ¢shes are nocturnal and orientate in the absence of vision by using their electrical sense. This enables them not only to navigate but also to perceive and recognize objects in complete darkness. They create an electric ¢eld around their bodies by producing electric signals with specialized electric organs. Objects within this ¢eld alter the electric current at electroreceptor organs, which are distributed over almost the entire body surface. During active electrolocation, ¢shes detect, localize and analyse objects by monitoring their self-produced electric signals. We investigated the ability of the mormyrid Gnathonemus petersii to perceive objects three-dimensionally in space. Within a range of about 12 cm, G. petersii can perceive the distance of objects. Depth perception is independent of object size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters (maximal slope and maximal amplitude) of the electrical image which each object projects onto the ¢sh's skin. During active electrolocation, electric ¢shes cannot only locate objects in space but in addition can determine the three-dimensional shape of an object. Up to certain limits, objects are spontaneously categorized according to their shapes, but not according to their sizes or the materials of which they are made.
Ethology, 2010
We investigated the electrolocation performance of the weakly electric fish, Gnathonernus petersiz, in novel and familiar environments. By selectively interfering with the fish's sensory input, we determined the sensory channels necessary for navigation and orientation. The fish's task was to locate a circular aperture (diameter: 64 mm) in a wall dividing a 200-1 aquarium into two equal compartments. To assess the fish's performance, we measured (1) the time it took the fish to locate the aperture, (2) the height at which it contacted the divider, (3) its electric organ discharge rate, and (4) the frequency of divider crossings. In the first experiment (novel environment), 50 naive G. petersii assigned to five groups of 10 fish each (intact, blind, electrically "silent," blind and "silent," and shamoperated animals) were tested with the aperture presented randomly in one of three positions (aperture center: 7.6, 17.7, 27.8 cm from the bottom). In a novel environment, G. petersii depend on active electrolocation. Despite the changing aperture position, over the 15 trials, fish with a functioning electric organ found the aperture, whereas those without one did not. The electric organ discharge rate was inversely correlated with the amount of time spent searching for the aperture. In a second experiment (familiar environment) 20 intact fish learned the position of a fixed aperture. When we subsequently denervated the electric organ in 10 of these animals, their performance did not differ significantly from that of their conspecifics. Thus, once the fish were familiar with the aperture's position, they no longer depended on active electrolocation. We interpret and discuss this behavior as evidence for a "central expectation" and discuss its possible role in electronavigation.
The functional roles of passive electroreception in non-electric fishes
Animal Biology, 2004
Passive electroreception is a complex and specialised sense found in a large range of aquatic vertebrates primarily designed for the detection of weak bioelectric elds. Particular attention has traditionally focused on cartilaginous shes, but a range of teleost and non-teleost shes from a diversity of habitats have also been examined. As more species are investigated, it has become apparent that the role of electroreception in shes is not restricted to locating prey, but is utilised in other complex behaviours. This paper presents the various functional roles of passive electroreception in non-electric shes, by reviewing much of the recent research on the detection of prey in the context of differences in species' habitat (shallow water, deep-sea, freshwater and saltwater). A special case study on the distribution and neural groupings of ampullary organs in the omnihaline bull shark, Carcharhinus leucas, is also presented and reveals that prey-capture, rather than navigation, may be an important determinant of pore distribution. The discrimination between potential predators and conspeci cs and the role of bioelectric stimuli in social behaviour is discussed, as is the ability to migrate over short or long distances in order to locate environmentally favourable conditions. The various theories proposed regarding the importance and mediation of geomagnetic orientation by either an electroreceptive and/or a magnetite-based sensory system receives particular attention. The importance of electroreception to many species is emphasised by highlighting what still remains to be investigated, especially with respect to the physical, biochemical and neural properties of the ampullary organs and the signals that give rise to the large range of observed behaviours.
Active electrolocation in Gnathonemus petersii: Behaviour, sensory performance, and receptor systems
Journal of Physiology-Paris, 2008
Weakly electric fish can serve as model systems for active sensing because they actively emit electric signals into the environment, which they also perceive with more than 2000 electroreceptor organs (mormyromasts) distributed over almost their entire skin surface. In a process called active electrolocation, animals are able to detect and analyse objects in their environment, which allows them to perceive a detailed electrical picture of their surroundings even in complete darkness. The African mormyrid fish Gnathonemus petersii can not only detect nearby objects, but in addition can perceive other properties such as their distance, their complex electrical impedance, and their three-dimensional shape. Because most of the sensory signals the fish perceive during their nightly activity period are self-produced, evolution has shaped and adapted the mechanisms for signal production, signal perception and signal analysis by the brain. Like in many other sensory systems, so-called prereceptor mechanisms exist, which passively improve the sensory signals in such a way that the signal carrier is optimized for the extraction of relevant sensory information. In G. petersii prereceptor mechanisms include properties of the animal's skin and internal tissue and the shape of the fish's body. These lead to a specific design of the signal carrier at different skin regions of the fish, preparing them to perform certain detection tasks. Prereceptor mechanisms also ensure that the moveable skin appendix of G. petersii, the 'Schnauzenorgan', receives an optimal sensory signal during all stages of its movement.
Ethology, 2010
We investigated the electric organ discharge (EOD) activity of the mormyrid fish Bvzenomyrus nzger during social encounters. The fish were contained in porous ceramic shelters and tested alone and in pairs in an experimental tank designed to restrict communication to the electrosensory modality. We moved one fish toward and away from a stationary conspecific, beginning at a distance known to be outside the range of communication (250 cm). Baseline E O D activity was recorded prior to interaction and categorized as 'variable', 'regular', and 'scallop'. When moved closer together, the fish modulated this baseline activity in four ways: (1) At 100-130 cm apart, the stationary fish emitted a maximum of sudden E O D rate increases which defined the outer limit of its communication range. (The associated Electric Field Gradient was 1 pV/cm). (2) Long E O D cessations, which we called social silence, lasted from 5-130 s and occurred most frequently when the fish were 36 to 55 cm apart (EFG: 100 pV/cm). The duration of social silence was negatively correlated (r =-0.862) with the responding fish's size, and was independent of the partner's sex and size. Fish whose E O D baseline pattern was 'scallop' were least likely to fall electrically silent, and those that were categorized as 'regular' or 'variable' were most likely to cease discharging. (3) Within electrolocation range, fish 'regularized' their E O D activity while the partner was 'silent' (EFG: 1 mV/cm). (4) Following long E O D cessations the fish resumed discharging with characteristic E O D rebound patterns. The possible ethological significance of these findings is discussed.
Animal Behaviour, 1973
The electric organ discharges (EODs) of pairs of weakly electric fish, Gnathonemus petersii, were simultaneously recorded to study the significance of the EODs as communication signals. In a 400-1itre tank a larger fish (i2 to 15 cm) was passively moved within a shelter tube toward a smaller specimen (6 to 9 cm), either in steps or a continuous move. The movement was stopped at that distance when at least one fish significantly lowered or ceased its EOD activity. From this 'threshold interfish distance' the spatial range of a 'communication field' was found to extend about 30 cm from the fish. At threshold distances an EOD frequency increase caused a temporary EOD activity cessation in the second fish. The spontaneous irregular EOD pattern of the fish displaying the increased EOD rate changed into a regular one with almost equal time intervals between fish pulses.
Discrimination of objects through electrolocation in the weakly electric fish, Gnathonemus petersii
Journal of Comparative Physiology A, 1990
Three weakly electric fish (Gnathonemus petersii) were force-choice trained in a two-alternative procedure to discriminate between objects differing in their electrical characteristics. The objects were carbon dipoles in plexiglass tubing (length 2.5 cm, diameter 0.6 cm). Their electrical characteristics could be changed by varying the impedance of an external circuit to which they were connected (Fig. 1). In one (the 'capacitance dipole') the resistance was very low (< 3 fl) and the capacitance variable. In the other (the 'resistance dipole') the resistance was variable and the capacitance low (< 50 pV). Capacitances from several hundred pF ('lower thresholds', Fig. 2) to several hundred nF ('upper thresholds', Fig. 3) could be discriminated from both insulators and good conductors. In all cases the rewardnegative stimulus was the capacitance dipole, which was avoided by all fish spontaneously. Thresholds were defined at 70% correct choices. The fish were then tested for their ability to discriminate between one object with a given capacitance and another with resistances varying from 3 [2 to 200 kf~. The capacitance dipole continued to be the negative stimulus throughout. All 3 fish avoided it in at least 80% of the trials at each stimulus combination (Fig. 4). This result suggests that Gnathonemus perceives the capacitance and the resistance of objects differentially. The effect of the dipole-objects as well as some natural objects on the local EOD was recorded differentially very close to the fish's skin (Fig. 5). The amplitude of the local EODs was affected by all types of objects as they approached the skin. However, the waveform was changed only by capacitance dipoles and some natural objects (Figs. 6 and 7). It appears that the fish perceive not only intensity changes in the local EOD but waveform deformations as well and can thus distinguish objects of different complex impedances.
Animal Behaviour, 1982
A characteristic electric organ discharge display in social encounters between mormyrid fish is a temporary discharge cessation. Using this response, we have investigated the useful range of electrocommunication under different water conductivity conditions in the mormyrid Brienomyrus niger. An individual fish was confined to a porous ceramic shelter tube and moved from a starting distance of 380 cm toward a similarly confined conspecific until discharge cessation occurred. The moved fish was subsequently returned to its original position. Water conductivity affects the peak-to-peak source voltage of the electric organ and the sensitivity of the fish's electroreceptors. Within a range of t0 to 36 000 gS/cm, the peak-to-peak amplitude of the electric organ discharge declined as a power function. At 120 pS/cm, the amplitude was 50%, and at 300 gS/cm, 30 ~ of the 10 pS/cm value. The interfish distance at which discharge cessation occurred and the associated electric field gradients were dependent on water conductivity and upon the spatial orientation of the two fish (end-to-end or parallel orientations of their shelter tubes). The respective ranges were from 135 cm and 0.02 mV/cm at 52 gS/cm (parallel orientation) to 22 cm and 0.36 mV/cm at 678 gS/cm (end-to-end orientation). When the data for both tube orientations were combined, the relationship between water conductivity (x) and the distance at which discharge cessation occurred (y) could be expressed by a power function, y = K. x" (with K = 10z.97 and a =-0.56). When an electrically 'silent' fish was moved away from its conspecific, a discharge resumption in the form of a high-frequency rebound occasionally effected changes in the other fish's discharge activity at distances up to 157 cm (with an associated electric field gradient of 0.01 mV/cm under the lowest conductivity condition).
Journal of Comparative Physiology A, 2004
Mormyrid fish use active electrolocation to detect and analyze objects. The electrosensory lateral line lobe in the brain receives input from electroreceptors and an efference copy of the command to discharge the electric organ. In curarized fish, we recorded extracellularly from neurons of the electrosensory lateral line lobe while stimulating in the periphery with either a local point stimulus or with a more natural whole-body stimulus. Two classes of neurons were found: (1) three types of E-cells, which were excited by a point stimulus; and (2) two types of I-cells, which were inhibited by point stimulus and responded with excitation to the electric organ corollary discharge. While all neurons responded to a point stimulus, only one out of two types of I-units and two of the three types of E-units changed their firing behavior to a whole-body stimulus or when an object was present. In most units, the responses to whole-body stimuli and to point stimuli differed substantially. Many electrosensory lateral line lobe units showed neural plasticity after prolonged sensory stimulation. However, plastic effects during whole body stimulation were often unlike those occurring during point stimuli, suggesting that under natural conditions electrosensory lateral line lobe network effects play an important role in shaping neural plasticity.