Electric organ discharge frequency jamming during social interactions in brown ghost knifefish, Apteronotus leptorhynchus

Abstract

In most communication systems, animals avoid jamming when similar signals from two individuals might overlap and cause interference. Most species of wave-type electric fish avoid jamming by shifting their electric organ discharge (EOD) frequencies away from those of conspecifics or away from mimics of sine wave EOD frequencies presented in playback experiments. Both male and female brown ghosts, however, appear to intentionally jam rivals during competitive interactions if the rival has a higher EOD frequency. We studied this behaviour in competitive interactions between two fish in a neutral arena, and in playback studies with single fish in resident–intruder and neutral arena models. During competitive interactions, females jammed the rival's EOD signal only when the rival's EOD frequency was within ∼30 Hz of their own EOD frequency, whereas males tried to jam EOD signals of rivals that were 70 Hz higher than their own EOD frequency. In the resident–intruder model experiment, fish tended to raise their EOD frequencies to within potential jamming range in response to a simulated intruder with a higher EOD frequency than their own. In a neutral arena model, fish directed the most aggressive attacks in response to simulated rivals with lower EOD frequencies, yet were less likely to attack the playback device if it played a frequency elevation that mimicked a fish with a lower EOD frequency attempting to jam them. This is the first evidence that electric fish may actively use jamming as an aggressive behaviour.