Active electroreception in Gymnotus omari: Imaging, object discrimination, and early processing of actively generated signals

2009

SUMMARYThis article shows that differences in the waveforms of the electric organ discharges (EODs) from two taxa are due to the different responsiveness of their electric organs (EOs) to their previous activity (auto-excitability). We compared Gymnotus omarorum endemic to Uruguay (35°South, near a big estuary), which has four components in the head to tail electric field (V 1 to V 4 ), with Gymnotus sp. endemic to the south of Brazil, Paraguay and Argentinean Mesopotamia (25°South, inland), which shows a fifth component in addition to the others (V 5 ). We found that: (a) the innervation pattern of the electrocytes, (b) the three earlier, neurally driven, EOD components (V 1 to V 3 ), and (c) their remnants after curarisation were almost identical in the two taxa. The equivalent electromotive forces of late components (V 4 and V 5 ) increased consistently as a function of the external current associated with the preceding component and were abolished by partial curarisation in both taxa. Taken together these data suggest that these components are originated in the responses of the electrocytes to longitudinal currents through the EO. By using a differential load procedure we showed that V 4 in G. omarorum responded to experimental changes in its excitation current with larger amplitude variations than V 4 in Gymnotus sp. We conclude that the differences in the EOD phenotype of the two studied taxa are due to the different EO auto-excitability. This, in turn, is caused either by the different expression of a genetic repertoire of conductance in the electrocyte membrane or in the wall of the tubes forming the EO.

Section: Discussionmentioning

confidence: 99%

Waveform diversity of electric organ discharges: the role of electric organ auto-excitability inGymnotusspp.

Rodríguez-Cattáneo

2009

“…Thus, this double-distance theory led to a new operative concept for analyzing image formation: the 'electric stamp' of the object. The electric stamp of an object corresponds to the set of electric sources that, if placed instead of the object, yields the same image (Caputi et al, 2008;Pereira and Caputi, 2010). Interestingly, theoretical results suggest that the stamp of an object and the object-perturbing field are dependent on different factors and thus they decay with distance at a different rate (Pereira, 2009;Pereira and Caputi, 2010).…”

Section: Introductionmentioning

confidence: 99%

The active electrosensory range ofGymnotus omarorum

Pereira

Aguilera

2012

SUMMARYThis article reports a biophysical and behavioral assessment of the active electrolocation range of Gymnotus omarorum. Physical measurements show that the stimulus field of a point on the sensory mosaic (i.e. the potential positions in which an object may cause a significant departure of the transcutaneous field from basal in the absence of an object) consists of relatively extended volumes surrounding this point. The shape of this stimulus field is dependent on the position of the point on the receptive mosaic and the size of the object. Although the limit of stimulus fields is difficult to assess (it depends on receptor threshold), departure from the basal field decays rapidly, vanishing at about 1.5 diameters for conductive spheres. This short range was predictable from earlier theoretical constructs and experimental data. Here, we addressed the contribution of three different but synergetic mechanisms by which electrosensory signals attenuate with object distance. Using novelty responses as an indicator of object detection we confirmed that the active electrosensory detection range is very short. Behavioral data also indicate that the ability to precisely locate a small object of edible size decays even more rapidly than the ability to detect it. The role of active electroreception is discussed in the context of the fishʼs habitat.

“…Nevertheless, an important clue could be the presence of movements of the fish or object. As stationary images are removed by the presence of an adaptive filter, probably at the electrosensory lobe Caputi et al, 2008), a fish may take advantage of relative movements in two ways: (1) use its own movements to maintain a closer conductive object stationary, working as a 'telescopic device' that artificially extends the fish's body and consequently increases the detection range; and (2) to better discriminate the attributes of a closer object in the presence of a moving context behind the object (as for example leaves and roots of water plants) (Babineau et al, 2007;Behr et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Active electrolocation in pulse gymnotids: sensory consequences of objects’ mutual polarization

Aguilera

Pereira

2012

Self Cite

SUMMARYWe examined non-linear effects of the presence of one object on the electric image of another placed at the foveal region in Gymnotus omarorum. The sensory consequences of object mutual polarization on electric images were also depicted using behavioral procedures. Image measurements show that objects whose electric image is not detectable may modify the electric image of another placed closer to the fish and suggest that detection range and discrimination parameters used for one object may be affected when the presence of others enriches the scene. Behavioral experiments confirm that these changes in object images resulting from mutual polarization may be exploited for improving perception. While conductive objects close to the skin allow the fish to detect other objects placed out of the active electrodetection range, non-conductive objects may hide objects that otherwise show clear electric images. This suggests that fish movements may orient the self-generated field to exploit object mutual polarization, increasing or decreasing the active electrolocation range. In addition, images of a nearby object may be modulated by the presence of another object placed outside the detection range and the corresponding behavioral responses suggest that a moving or impedance-changing context may modify a fishʼs discrimination abilities for closer objects.