How well do electric fish electrolocate under jamming?
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In two species of weakly electric fish, electrolocation performance and its vulnerability to electrical noise were assessed through behavioral experiments, providing the following results.
In contrast to all other wave-emitting electric fish,Sternopygus does not exhibit a Jamming Avoidance Response (JAR), i.e., it does not shift its Electric Organ Discharge (EOD) frequency away from either a conspecific's or an electronic generator signal's frequency which is sufficiently close to its own EOD frequency.
Sternopygus' lack of a JAR, a mechanism known to protect electrolocation abilities in other electric fish, is adaptively correlated with an unusual “immunity” of its electrolocation performance to jamming signals. It is only with strong sinusoidal stimulus intensities, as great as 50 times stronger than the fish's own near field EOD intensity, that impairment of electrolocation performance begins inSternopygus. In contrast, electrolocation performance inEigenmannia is greatly impaired by stimuli as weak as the animal's own near field EOD intensity.
BothSternopygus (given stimuli of sufficient intensity) andEigenmannia are most vulnerable to stimulus frequencies which differ slightly from their own EOD frequency; i.e., whenΔF=1 to 4 Hz (Figs. 2,3). However, in both genera electrolocation performance improves forΔFs=0 Hz (inaccuracy of 0.016 Hz); in this case, with amplitudes equal to its near field intensity,Eigenmannia's electrolocation performance improves almost to levels observed in the absence of jamming (Fig. 3). These results provide a behavioral correlate not only to predictions based on theoretical models but also to previous neurophysiological studies on central electroreceptive units.
KeywordsTheoretical Model Generator Signal Field Intensity Stimulus Intensity Behavioral Experiment
Jamming Avoidance Response
Electric Organ Discharge
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