Lorenzo, D. & O. Macadar. 2005. Influence of temperature and reproductive

state upon the jamming avoidance response in the pulse-type electric fish

Brachyhypopomus Pinnicaudatus. Journal of Comparative Physiology.

191: 85–94.

This study quantifies the variation in ability of Brachyhypopomus pinnicaudatus males to generate JAR in response to fluctuating temperatures similar to those experienced by wild populations. The authors assessed the response of three groups of males to interfering electric pulses. Six non-reproductive males, six ‘acclimated’ reproductive males (reproductive state induced by heat and light alterations), and 5 naturally reproductive males were exposed to a 20ºC treatment and a 30ºC treatment in which interfering EODs were delivered by electrodes 5 cm from the test male. The interfering EODs were delivered by different methods in two separate trials.

In the first trial, males were exposed to ‘Free-run stimuli’ in which the interfering electric pulses were delivered at eight different ∆L values (difference in time between basal EOD and interference stimuli). This protocol allowed the authors to quantify JAR by measuring the magnitude of the transient interval decrease (TID: a TID is characterized as a reduction in EOD interval). In the second trial, males experienced ‘Phase-locked stimuli’ in which the interfering electric pulses were phase-locked to the EOD of the individual and were delivered continuously with a pulse duration of 1 s. The phase of the interfering wave was then increased systematically to see if this altered the detection window (DW: the interval of time in which the fish is sensitive and receptive to the interfering wave).

The authors found a substantial JAR for all groups of males at 20ºC. For the non-reproductive fish group, the interfering waves did not elicit JAR when temperature was raised. In contrast, both groups of reproductive fish could still perform JAR after the temperature was raised to 30ºC (in many cases the JAR was of greater magnitude as well). Furthermore, the authors found that the increase in temperature decreased the detection window (DW) for non-reproductive males but increased the DW for both groups of reproductive males. These combined results illustrate that reproductive fish have a greater ability to perform JAR in fluctuating temperatures.

In lecture, we discussed that the JAR behavior is adaptive for reproductively active males because it prevents masking of individual signals, so that each male (or at least the dominant male) can continue to signal to potential mates in the presence of interference. It makes sense then, that reproductive fish can generate JAR at a larger range of temperatures than non-reproductive fish as demonstrated by this study. Although in class we mainly discussed the adaptive significance of JAR, this study attempts to elucidate the mechanisms involved in this behavior as well. The study showed that the magnitude of JAR is dependent upon the water temperature; an increase in water temperature increases the window of time in which the fish is sensitive to interfering calls. (This is thought to be accomplished by sex hormones which also increase in response to higher temperatures). When discussing Fourier analysis, we learned that with a longer window of sound reception, a better estimation of frequency could be made. By applying this principle to electro-communication, we would predict that when a fish can more accurately estimate the EOD frequency of an interfering sound, it could more efficiently avoid it. Therefore, it’s possible that the increase in temperature allows the fish to better perceive the frequency of an interfering EOD, thus resulting in a more efficient JAR.