Influence of temperature and reproductive state upon the jamming avoidance response in the pulse-type electric fish Brachyhypopomus pinnicaudatus

The electric organ discharge (EOD) in Brachyhypopomus pinnicaudatus is modified by temperature and reproductive state. We studied the influence of these variables upon a complex behavior, the jamming avoidance response ( JAR). Experiments were performed in non-reproductive fish and in two groups of fish after the induction of reproductive state ( by nature or by acclimation at 28 degreesC). JARs were elicited at 20 and 30 degreesC by free-run electric stimuli with different DeltaLs ( interval difference between stimulus and EOD). In non-reproductive fish, JARs induced by stimuli with + DeltaLs showed temperature sensitivity, with smaller responses at 30 degreesC. Conversely, similar JARs were obtained at both temperatures in reproductive fish. These observations were replicated in curarized preparations. Stimuli with -DeltaLs were almost ineffective in non-reproductive fish at 30 degreesC, whereas adequate JARs were shown by reproductive fish. Phase-locked stimuli were used to evaluate the duration of the low-threshold electrosensory periods preceding and following the EOD. In non-reproductive fish,the temperature step induced a shortening of these periods. The opposite effect was observed in reproductive fish, probably explaining the differences in JAR capability. A prolongation of the low-threshold periods would favor the perception of electrocommunication signals during courtship. JAR changes would be a consequence of this adaptation.