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 degrees C). JARs were elicited at 20 and 30 degrees C 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 degrees C. 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 degrees C, 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.