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First published online May 2, 2008
Journal of Experimental Biology 211, 1657-1667 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013516
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Electrocommunication signals in free swimming brown ghost knifefish, Apteronotus leptorhynchus

Ginette J. Hupé* and John E. Lewis

Department of Biology and Centre for Neural Dynamics, University of Ottawa, Ottawa, ON, K1N 6N5, Canada


Figure 1
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  		Fig. 1. (A) Experimental design; the short, vertical lines indicate the position of the recording electrodes in the 9.5 l tank, the additional short, vertical line in the back right corner indicates the position of the ground electrode. (B) Oscillogram of a representative Type 2 chirp recorded from an isolated fish. Note that its duration, indicated by the period of amplitude modulation, is 15–20 ms. (C) An instantaneous frequency plot corresponding to the same Type 2 chirp as illustrated in B. Instantaneous frequency values were derived by taking the inverse of the cycle length, calculated as the duration between consecutive downstroke zero-crossings. (D) A spectrogram displaying the same Type 2 chirp as illustrated in B,C). (E) A spectrogram showing a representative Type 2 chirp (on the left) and a Type 1 chirp (on the right) recorded during a dyadic interaction. The higher frequency of two fish (877 Hz) is modulating its electric organ discharge frequency (EODf) to produce these chirps, whereas the lower frequency fish (714 Hz) does not modulate its EODf during this segment of the interaction. Note that the Type 2 chirp is associated with a much smaller frequency excursion than is the Type 1 chirp. (F) Spectrogram showing two abrupt frequency rises (AFRs) produced in succession by the lower frequency of two interacting fish; the third harmonics are shown and during this segment of the recording the EOD of the higher frequency fish is relatively weak, allowing for a clearer representation of the EOD modulations of the other. Both of the AFRs shown consist of multiple distinct and consecutive small frequency rises. For display purposes, the low amplitude components of each spectrogram were removed and only the strongest (10–20%) amplitude components are shown.

 

Figure 2
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  		Fig. 2. Type 1 chirps (A) and Type 2 chirps (B) are produced at sexually dimorphic rates. AFRs (C) are not produced at sexually dimorphic rates. Values are means (± s.e.m.) for males and females, averaged across all trials (N=42).

 

Figure 3
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  		Fig. 3. The effect of the absolute difference frequency (Df) on signal production rates for Type 2 chirps (A) and AFRs (B). (A) Type 2 chirps are classified by sex pairing; the Type 2 chirp rates of males paired with a second male (squares; N=16, R2=0.21), and of males paired with a female (diamonds; N=9, R2=0.860). (B) AFRs in which all fish were pooled because there were no differences across the different sex pairings (N=42, R2=0.14). Linear regressions are shown.

 

Figure 4
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  		Fig. 4. Chirp (A) and attack (B) rates change with time. Mean (± s.e.m.) chirp and attack counts, binned into 30 s intervals, are shown. With respect to Type 2 chirps, only male counts were included (N=25); whereas for attacks, all fish were pooled (N=42).

 

Figure 5
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  		Fig. 5. Inter-chirp interval histogram with totals for all males tabulated over all trials (N=24, one male was excluded because he only produced one chirp). The preferred inter-chirp latency is 400–600 s.

 

Figure 6
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  		Fig. 6. Upper panels: auto-correlograms illustrate signal patterning of a single fish for (A) Type 2 chirps (N=22), (B) AFRs (N=31) and (C) Type 2 chirps and AFRs (N=18). Means for all fish for all trials in which fish produced 10 or more signals are plotted, except in the case of Type 2 chirps where only male counts are used in the analysis. The horizontal line denotes the null distribution: the distribution expected if signals are produced at random. Lower panels: bin-by-bin statistical analysis of the correlograms. The fraction of individual fish in which the corresponding bin height is either greater than expected by chance (P>0.95, black line) or less than expected by chance (P<0.05, grey line).

 

Figure 7
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  		Fig. 7. Upper panels: cross-correlograms illustrate signal relationships between fish for (A) Type 2 chirps (N=14), (B) AFRs (N=22), and (C) Type 2 chirps and AFRs (N=16). Means for all fish for all trials in which fish produced 10 or more signals are plotted, except in the case of Type 2 chirps where only male counts are used in the analysis. Horizontal line denotes the null distribution. Lower panels: bin-by-bin statistical analysis of the correlograms. The fraction of individual fish in which the corresponding bin height is either greater than expected by chance (P>0.95, black line) or less than expected by chance (P<0.05, grey line).

 

Figure 8
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  		Fig. 8. Upper panel: cross-correlogram relating Type 2 chirp production with attack counts are given for (A) a single fish (N=16) and (B) between fish (N=10). Only male fish, and trials involving 10 or more chirps and attacks are used in the chirp-attack analysis. Horizontal line denotes the null distribution. Lower panels: bin-by-bin statistical analysis of the correlograms. The fraction of individual fish in which the corresponding bin height is either greater than expected by chance (P>0.95, black line) or less than expected by chance (P<0.05, grey line).

 

Figure 9
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  		Fig. 9. Upper panel: cross-correlogram relating AFR production with attack counts are given for (A) a single fish (N=19) and (B) between fish (N=16) for all trials involving 10 or more AFRs and attacks. Horizontal line denotes the null distribution. Lower panels: bin-by-bin statistical analysis of the correlograms. The fraction of individual fish in which the corresponding bin height is either greater than expected by chance (P>0.95, black line) or less than expected by chance (P<0.05, grey line).

 

Figure 10
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  		Fig. 10. Inter-fish distance centred at the time of signal production for (A) Type 2 chirps (N=25) and (B) AFRs (N=39). The inter-fish distances represent the distance from one fish's snout to the other fish's snout. Means ± s.e.m. are plotted for males only in the case of Type 2 chirps, and all fish in the case of AFRs.

 

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© The Company of Biologists Ltd 2008