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First published online November 17, 2006
Journal of Experimental Biology 209, 4809-4818 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02579
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Structure and sexual dimorphism of the electrocommunication signals of the weakly electric fish, Adontosternarchus devenanzii

Muchu Zhou1 and G. Troy Smith1,2,3,*

1 Department of Biology, Indiana University, Bloomington, IN 47405, USA
2 Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA
3 Program in Neuroscience, Indiana University, Bloomington, IN 47405, USA


Figure 1
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  		Fig. 1. EOD modulations in A. devenanzii (A,C-E) and A. leptorhynchus (B). (A) Scatter plot of the frequency modulation (FM, Hz) and duration (s) of 1286 EOD modulations recorded from 11 male and eight female A. devenanzii. Two types of EOD modulations could be distinguished based on the degree of FM: chirps (squares) and gradual frequency rises (GFRs, circles). Chirps and GFRs could have either single frequency peaks (open symbols) or multiple frequency peaks (grey symbols). Note that because so many chirps are plotted, many single-peaked chirps and GFRs are obscured by overlying multi-peaked chirps and GFRs. (B) A comparable plot for 7950 EOD modulations from A. leptorhynchus based on data from Kolodziejski et al. (Kolodziejski et al., 2005Go). A. leptorhynchus produces GFRs (circles) and two types of chirps: high-frequency chirps (squares) and low-frequency chirps (triangles). Note the absence of low-frequency chirps in Adontosternarchus and the lack of multi-peaked modulations in A. leptorhynchus. (C) Histogram of the duration of single-peaked chirps. Although most single-peaked chirps lasted 0.02-0.08 s, there is a `tail' of longer duration chirps. (D) Histogram of the duration of multi-peaked chirps in A. devenanzii. (E) Examples of single- and multi-peaked chirps and GFRs produced by A. devenanzii. The top trace in each example tracks EOD frequency, and the bottom trace is the raw voltage record. Note the different time and frequency scales for chirps and GFRs.

 

Figure 2
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  		Fig. 2. Numbers of each type of EOD modulation produced (mean ± s.e.m.) by male (white bars) and female (grey bars) A. devenanzii. The P-values for significant or marginally insignificant sex differences (unpaired t-tests) are indicated above the bars.

 

Figure 3
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  		Fig. 3. Effect of stimulus difference frequency (i.e. the difference between the subject fish's EOD frequency and the stimulus frequency) on the number of chirps (A) and GFRs (B). The numbers of multi-peaked chirps and multi-peaked GFRs are indicated by broken lines, and the total numbers of chirps and GFRs by solid lines. Stimulus frequency did not significantly affect the number of any of these EOD modulations.

 

Figure 4
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  		Fig. 4. Partial phylogeny of wave-type gymnotiform fish, illustrating evolution of electrocommunication signals and their sexual dimorphism. Phylogeny based on Crampton and Albert (Crampton and Albert, 2006Go). Comparison of electrocommunication signals based on this study and published reports (Hopkins, 1974bGo; Hopkins, 1974cGo; Meyer, 1983Go; Hagedorn and Heiligenberg, 1985Go; Dye, 1987Go; Zupanc and Maler, 1993Go; Dunlap and Zakon, 1998Go; Dunlap et al., 1998Go; Dunlap and Larkins-Ford, 2003Go; Kolodziejski et al., 2005Go). `X', presence of the trait; `O', absence of the trait; `?', either the trait has not been investigated or the data are equivocal. 1Long- and short-duration interruptions in Eigenmannia may be analogous to high- and low-frequency chirps in Apteronotus (Hagedorn and Heiligenberg, 1985Go; Hopkins, 1974cGo). 2A. albifrons can produce GFRs and chirps that have complex spectro-temporal structure (Dunlap and Larkins-Ford, 2003Go; Serrano-Fernandez, 2003Go), but they are rare and are not similar to the multi-peaked chirps and GRFs of A. devenanzii. 3Hopkins recorded EOD modulations in only one female Sternopygus and it is thus unclear whether EOD modulations are sexually dimorphic in this genus (Hopkins, 1974bGo). 4Data from Hopkins (Hopkins, 1974cGo) and Hagedorn and Heiligenberg (Hagedorn and Heiligenberg, 1985Go) suggest sex differences in the number and/or structure of interruptions and rises, but statistical analyses were not reported. A, lower EOD frequencies in males than females; B, gradual frequency rises (GFRs); C, EOD modulations differentially depend on EOD frequencies of other fish; D, chirping; E, distinct high- and low-frequency chirps; F, higher EOD frequencies in males than females; G, sex difference in number of EOD modulations; H, short-duration chirps; I, high-frequency chirps with frequency undershoots; J, loss of sex difference in EOD frequency; K, multi-peaked chirps and GFRs common; L, more multi-peaked chirps produced by males; M, loss of differential production of EOD modulations based on EOD frequencies of other fish.

 

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© The Company of Biologists Ltd 2006