Stereotyped temporal patterns in electrical communication

Mormyrid electric fish communicate using a fixed electric organ discharge (EOD) produced with a variable sequence of pulse intervals (SPI). Through a combination of spike train analysis techniques and multivariate statistics, we develop quantitative methods for analysing temporal patterns in the SPI in Brienomyrus brachyistius. Previous research has indicated the existence of distinct temporal patterns that play an important role in social behaviour, but these studies have relied upon subjective assessments of the SPI: no study has yet used quantitative methods for analysing temporal patterns, so it remains unclear whether there are categorically distinct displays or continuous variation. We demonstrate the existence of three modal classes of frequency modulations (bursts) that differ categorically in their temporal patterning and can therefore be appropriately termed displays. 'Scallops' are stereotyped, transient bursts to EOD intervals of 10-20 ms. 'Accelerations' are maintained decreases in EOD interval to values of 25-40 ms. Evidence indicates that 'rasps' combine a scallop followed by an acceleration. Analysis of signal characteristics and their production in relation to several variables, combined with previous research, suggests that accelerations function as aggressive signals, rasps as male courtship signals, and scallops as advertisement signals. This descriptive study is an important first step in the analysis of temporal patterns in the SPI, and provides a foundation for addressing general issues in animal communication. The relative simplicity of their electric communication displays suggest that mormyrids are an excellent model system for studying the evolution, function and mechanisms of stereotyped temporal pattern generation.