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First published online June 29, 2007
Journal of Experimental Biology 210, 2501-2509 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005272

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Stimulus frequency differentially affects chirping in two species of weakly electric fish: implications for the evolution of signal structure and function

Johanna A. Kolodziejski^1,2,*, Sara E. Sanford^2,3 and G. Troy Smith^1,2,4

¹ Department of Biology, Indiana University Bloomington, Bloomington, IN 47405, USA
² Center for the Integrative Study of Animal Behavior (CISAB), Indiana University Bloomington, Bloomington, IN 47405, USA
³ Department of Psychology, Emory University, 532 Kilgo Circle, Atlanta, GA 30322, USA
⁴ Program in Neuroscience, Indiana University Bloomington, Bloomington, IN 47405, USA

View larger version (10K): [in this window] [in a new window]   Fig. 1. Number of chirps (A) and rises (B) (mean ± s.e.m.) produced during playback stimulation as a function of difference frequency (Df) in A. leptorhynchus (N=20, open squares) and A. albifrons (N=31, closed circles). (A) Both species produced significantly more chirps (low- and high-frequency chirps combined) in response to stimuli close in frequency to their own EOD (within 20 Hz) than to distant frequencies (±150 Hz). (B) There was no effect of Df on the number of rises (long-duration modulations) produced by either species. Data points with different letters differ significantly from each other; Tukey's HSD, P<0.05. NS, no significant effect of Df (repeated-measures ANOVA, P>0.05).

View larger version (10K): [in this window] [in a new window]   Fig. 2. Number of low-frequency chirps (mean ± s.e.m.) produced during playback stimulation as a function of Df in male (A) and female (B) A. leptorhynchus (open squares) and A. albifrons (closed circles). (A) Male A. leptorhynchus (N=11, open squares) produced more low-frequency chirps to stimuli close in frequency to their own EOD (within 20 Hz) than to distant frequencies (±150 Hz). Similarly, A. albifrons males (N=16, closed circles) produced more low-frequency chirps to stimuli 5 Hz lower than their own EOD compared to stimuli 150 Hz higher or lower. (B) There was no effect of Df on the production of low-frequency chirps in A. leptorhynchus females (N=9, open squares), although the trend was similar to the overall effect of Df seen in males. Female A. albifrons (N=15, closed circles) produced more low-frequency chirps to stimuli within 5 Hz of their own EOD than stimuli 150 Hz lower or higher. Data points with different letters differ significantly from each other; Tukey's HSD, P<0.05. NS, no significant effect of Df (repeated-measures ANOVA, P>0.05).

View larger version (11K): [in this window] [in a new window]   Fig. 3. Number of high-frequency chirps (mean ± s.e.m.) produced during playback stimulation as a function of Df in male (A,B) and female (C,D) A. leptorhynchus (A,C) and A. albifrons (B,D). (A) Male A. leptorhynchus (N=11) produced significantly more high-frequency chirps to the –150 Hz Df than to the –5 Hz Df. (B) In a pattern opposite to that seen in A. leptorhynchus, male A. albifrons (N=16) produced significantly more high-frequency chirps to same-sex stimuli (within 20 Hz) than to opposite sex stimuli (±150 Hz). (C) Female A. leptorhynchus (N=9) produced almost no high-frequency chirps, and Df did not affect their production. (D) There was no effect of Df on the number of high-frequency chirps produced by female A. albifrons (N=15), although the trend was similar to the effect of Df seen in males. Data points with different letters differ significantly from each other Tukey's HSD, P<0.05. NS, no significant effect of Df (repeated-measures ANOVA, P>0.05).

View larger version (11K): [in this window] [in a new window]   Fig. 4. Number of chirps (A) and rises (B) (mean ± s.e.m.) produced before (S, spontaneous), during (E, evoked), and after (P, post-stimulus) stimulus presentation. (A) Both A. leptorhynchus and A. albifrons produced more chirps during stimulation (E) than before stimulus onset (S) or after stimulus offset (P). (B) Both species produced more rises after stimulus offset (P) than before stimulus onset (S) or during stimulus presentation (E). Data points within each species that have different letters differ significantly from each other; Tukey's HSD, P<0.05.