Phase sensitivity and phase coupling: Common mechanisms for communication behaviors in gymnotid wave and pulse species

Summary

• 1. Stimulation of Eigenmannia with signals locked to various phases of the EOD cycle yielded a profile of phase sensitivity. A phase range where stimuli produced sharp increase of frequency could be distinguished from a range where frequency decrease was clicited (Figs. 2 and 3).

• 2. The position of the boundaries between frequency accelerating and decelerating effects on the phase scale was dependent on the stimulus wave form (Figs. 2 and 3).

• 3. Eigenmannia phase coupled its EOD to stimuli with a frequency difference (ΔF) below 1 Hz. Coupling occurred preferentially close to the beat maximum and to the minimum (Figs. 4 and 5).

• 4. Coupling occurred starting from an initial positive or negative ΔF of the stimulus, though there were individual preferences for one or the other sign of the ΔF. Coupling was commonly terminated by a jamming-avoidance response (Figs. 4 and 5).

• 5. Phase coupling was seen as well in two species of Apteronotus, in Sternopygus, and in the pulse fish Rhamphichthys. In all species there was a preference for particular phase ranges. Within the ranges, small phase oscillations were common (Fig. 6).

• 6. All species showed coupling to Δ2 F signals (double frequency of the EOD); Eigenmannia and Sternopygus only coupled to Δ1/2 F signals (half the EOD frequency) if the stimulus wave form was adjusted to a normal EOD in that frequency range.