ZHOU, M.; SMITH, G.T.; Indiana Univ., Bloomington; Indiana Univ., Bloomington: Electrocommunication signals of Adontosternarchus balaenops

Apteronotid knifefish produce a weak electric organ discharge (EOD) for electrolocation, and modulate the frequency of this discharge to produce “chirps,” which are used as communication signals. Electrocommunication in most species studied to date is sexually dimorphic. In Apteronotus leptorhynchus, the EOD frequency of males is higher than that of females, while the reverse is true in A. albifrons. Unlike A. albifrons, A. leptorhynchus also exhibits a sex difference in chirp rate and structure. In this study, we examined electrocommunication behavior of another apteronotid, Adontosternarchus balaenops, by measuring the EOD frequency of fish of both sexes and recording both spontaneous and playback-evoked chirping behavior. A. balaenops produced three distinct types of chirps: H-type and L-type chirps were both short in duration (101�10.8 ms, 158�16.3 ms) and exhibited large (151.5�1.6 Hz) and small (7.8�1.0 Hz) frequency excursions, respectively, and W-type chirps were intermediate in frequency excursion and were distinguished by a much longer duration (>1 s). Although the three chirp types were distinct, significant variation in chirp parameters were observed within each category, and the fish also produced other distinctive EOD modulations. Preliminary results indicate that, unlike in previously studied Apteronotus species, EOD frequency does not differ significantly between the sexes in A. balaenops. The total number of chirps produced was not sexually dimorphic in A. balaenops, but females produced a greater proportion of L-type chirps than males, suggesting that chirping behavior, but not EOD frequency, is sexually dimorphic in this species. Questions remain on how the different types of EOD modulations produced by A. balaenops are used during social interactions, and on the neural mechanisms responsible for these EOD behaviors.