Behavioural relevance of AC and DC in prey detection by the brown bullhead, Ameiurus nebulosus

Abstract

A large range of aquatic vertebrates employs passive electroreception to detect the weak bioelectric fi elds that surround their prey. Bioelectric fi elds are dynamic in strength and frequency composition, but typically consist of a direct current (DC) and an alternating current (AC) component. We examined the biological relevance of these components for prey detection behaviour in the brown bullhead by means of a preference test. We gave each fi sh the choice between two small dipoles emitting a DC step or AC stimulus of variable strength, respectively. We used AC stimuli that were either representative for venti latory movements by prey (1 Hz sine wave) or optimal for the ampullary electroreceptor cells (10 Hz sine wave). In an attempt to present a more complex stimulus, we also used slightly modifi ed recordings of bioelectric prey fi elds, but this yielded no results. Brown bullheads prefer DC stimuli to 10 Hz sine waves if the stimulus intensity of either component is much larger. When the stimulus presentation consists of DC versus 1 Hz, most fi sh will choose randomly unless the stimulus intensities diff er greatly. Th en, they favour the component that had a higher amplitude during training. Our results suggest an intrinsic behavioural preference for very low frequency signals (<10 Hz) as well as plasticity in prey detection behaviour.

Passive electroreception in bottlenose dolphins (Tursiops truncatus): implication for micro- and large-scale orientation

“…We have little insight into the physiology of electroreception in toothed whales, but it is interesting that the ratio of detectability of DC and AC fields in dolphins is similar to that in elasmobranchs. Naturally occurring bioelectric fields can be described as dynamic electric fields consisting of a standing DC-dipole electric field modulated by low-frequency AC components arising, for example, from ion exchange processes and gill respiratory movements ( Bedore and Kajiura, 2013 ; Bodznick et al, 1992 ; Eeuwes et al, 2008 ; Haine et al, 2001 ; Kalmijn, 1972 , 1974 ; Wilkens and Hofmann, 2005 , 2008 ). Several studies have shown that sharks and rays respond best to DC electric field signals, but also to low-frequency AC potentials <20 Hz ( Eeuwes et al, 2008 ; Kalmijn, 1971 , 1974 ; Kimber et al, 2011 ).…”

“…Naturally occurring bioelectric fields can be described as dynamic electric fields consisting of a standing DC-dipole electric field modulated by low-frequency AC components arising, for example, from ion exchange processes and gill respiratory movements ( Bedore and Kajiura, 2013 ; Bodznick et al, 1992 ; Eeuwes et al, 2008 ; Haine et al, 2001 ; Kalmijn, 1972 , 1974 ; Wilkens and Hofmann, 2005 , 2008 ). Several studies have shown that sharks and rays respond best to DC electric field signals, but also to low-frequency AC potentials <20 Hz ( Eeuwes et al, 2008 ; Kalmijn, 1971 , 1974 ; Kimber et al, 2011 ). Rays ( Raja clavata ) only showed good detection capabilities for AC fields of 16 and 32 Hz after increasing the electric field strength by factors of 8 and 32, respectively ( Kalmijn, 1974 ), whereas two shark species ( Scyliorhinus canicula and Triakis semifasciata ) no longer responded to AC stimuli with frequencies >16 Hz ( Kalmijn, 1973 , 1974 ).…”

“…Instead of the more frequently used sinusoidal signals (e.g. Eeuwes et al, 2008 ; Peters and Evers, 1985 ), we decided to use square-wave signals, as, for example, in the studies by Dijkgraaf and Kalmijn (1963) , Fields et al (1993) and Kalmijn (1966) , because of the better reproducibility using standard timing circuits. The root mean square (RMS) value of square-wave signals is approximately 30% higher compared with sinusoidal signals with the same frequency and amplitude, which could influence the determination of the sensory detection threshold.…”