Social electric signals in freely moving dyads of Brachyhypopomus pinnicaudatus.

Brachyhypopomus pinnicaudatus (pulse-type weakly electric fish) is a gregarious species that displays reproductive behavior and agonistic encounters between males only during the breeding season. During social interactions, in addition to its basal electric organ discharge (EOD), fish emit social electric signals (SESs) in the contexts of reproduction and intrasexual aggression. We reproduced natural behavior in laboratory settings: SESs recorded in the field are indistinguishable from those observed in our experimental setup. SESs are nocturnal, change seasonally and exhibit sexual dimorphism. This study provides an exhaustive characterization and classification of SESs produced by males and females during the breeding season. In male-female dyads, males produce accelerations and chirps while females interrupt their EODs. The same SESs are observed in male-male dyads. We present a novel, thorough classification of male chirps into four independent types (A, B, C, and M) based on their duration and internal structure. The type M chirp is only observed in male-male dyads. Chirps and interruptions, both in male-female and male-male dyads, are emitted in bouts, which are also grouped throughout the night. Our data suggest the existence of a sophisticated electric dialog during reproductive and aggressive interaction whose precise timing and behavioral significance are being investigated.