Harmonic and temporal structure of electric organ discharges of the wave-type in Amazonian knifefishes (Gymnotiformes)
Neotropical, nocturnal freshwater knifefishes of the families Sternopygidae and Apteronotidae are electroreceptive, and emit electric organ discharges (EODs) of the wave type for communication and active electrolocation. In a field-collected sample of an estimated 43 gymnotiform species, members of the former family displayed the same type of sinusoidal EOD waveform at frequencies of up to about 800 Hz, with the fundamental frequency, f1, the strongest harmonic in each. Members of the latter (Apteronotidae) displayed f1 frequencies of up to 1800 Hz, and a great diversity in EOD waveform. Apteronotid EODs often differed from those of sternopygids by more harmonics at stronger amplitudes, where f1 was not always the strongest harmonic. The frequency band at −10 dB increased with diminishing f1 amplitude. In contrast to apteronotids, all sternopygids showed the same phase relationship between their respective f1 and f2: a difference of an average 72°, which explains their single type of sinusoidal waveform. In apteronotids a great variety of phase relationships among harmonics was observed, in some their harmonics series cycled through 360° repeatedly. It is argued that the evolutionary driving force for the apteronotids — in contrast to sternopygids — was the greater potential for adaptive radiation.
KeywordsSignal waveform Amplitude spectrum Phase spectrum Sternopygidae Apteronotidae Total harmonic distortion Evolutionary driving force Carrier frequency
This study was instigated by the late Professor Hubert Markl who also took part in the field study. The host institution at Manaus was the Instituto Nacional de Pesquisas da Amazônia (INPA), and basic support provided by Dr. W.E. Kerr (Director), Dr. W.J. Junk and staff of the ichthyological department. Frank Kirschbaum assisted in catching and determining the fishes. I owe thanks and gratitude to all.
This study was funded by Deutsche Forschungsgemeinschaft, grants Ma 374/10, Kr 446/8, and associated travel grants for the field study in Brazil.
Compliance with ethical standards
Conflict of interest
The author declares that he has no conflict of interest.
All applicable international, national and institutional guidelines for the care and use of animals were followed.
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