Temporal spacing of signals in communication, studied in weakly-electric mormyrid fish (teleostei, pisces)

Abstract

Both the shape of the electric pulses and their rhythm of emission serve in communication in weakly-electric mormyrid fish. Because the pulses emitted by a given individual show very little variability, whereas the rhythm of emission is highly variable, the mormyrids electric emission can be considered to be the repetition according to various temporal spacings of the same signal. It allows therefore to study the role of the temporal spacing of signals in communication. The temporal spacing of the pulses could serve at a global level, in allowing the effects of consecutive pulses to summate. It could also be itself part of higher-order signals. In order to discriminate between these two possibilities, sequences of a conspecific's electric emission were played back to the mormyrid fish Gnathonemus petersii . The importance of the temporal spacing of the pulses at a global level was investigated by comparing the effects of (a)- 3 sequences of similar overall rate of discharge, (b)- 2 sequences of same rate of discharge plus same composition in interpulse intervals. Sequences of similar mean frequency (14 +/- 1 Hz) elicited different responses, showing they had different communicative values. Sequences having both the same interval composition and the same mean frequency elicited reactions which presented similarities, showing that the communicative value of the electric emission does nevertheless depend on the spacing of the pulses at a global level. The presence of higher order signals was investigated by testing the importance of the serial ordering of the intervals in electric emission. Randomisation of the intervals did alter the effect of a sequence, suggesting the existence of such signals. We showed that both the global composition in intervals and their serial ordering are relevant to electrocommunication in mormyrids. Thus, their communication system constitutes a useful model for the study of the transformation of sequences of simple signals into higher-order signals.