Variations in the electrocommunication behaviour of the weakly electric fish Apteronotus Leptorhynchus

Abstract

Apteronotus leptorhynchus (Gymnotiformes) is a weakly electric fish which produces wave-like electric organ discharges as well as brief modulations in the frequency of these discharges, termed chirps. Thought to be used for communicating, this study explores variations in previously described chirp types by investigating fish chirping behaviour through recordings of external electric field modulations, and several novel phenomena were characterized. An alternative form of the type 1 chirp was discovered that is preceded by a gradual rise in frequency lasting 8-10 ms. Two sub-categories of type 2 chirps emerged, distinguished by frequency excursions of 23-86 Hz and 86-183 Hz respectively, and individual fish chirp almost exclusively within a single subgroup. Type 3 chirps occupied a much lower range of durations (10-60 ms) than those previously described, and no type 4, 5 or 6 chirps were observed. Finally, a single unusual chirp characterized by an extreme frequency and amplitude modulation raises interesting questions about chirp production mechanisms. While we cannot exclude that the differences observed across chirping studies are a consequence of subtle differences in methodology, we propose that geographical variation in electrocommunication behaviour should be investigated as an alternative explanation with possible implications for speciation.