Abstract
Mormyrid weakly electric fish produce short, pulse-type electric organ discharges for actively probing their environment and to communicate with conspecifics. Animals emit sequences of pulse-trains that vary in overall frequency and temporal patterning and can lead to time-locked interactions with the discharge activity of other individuals. Both active electrolocation and electrocommunication are additionally accompanied by stereotypical locomotor patterns. However, the concrete roles of electrical and locomotor patterns during social interactions in mormyrids are not well understood. Here we used a mobile fish dummy that was emitting different types of electrical playback sequences to study following behavior and interaction patterns (electrical and locomotor) between individuals of weakly electric fish. We confronted single individuals of Mormyrus rume proboscirostris with a mobile dummy fish designed to attract fish from a shelter and recruit them into an open area by emitting electrical playbacks of natural discharge sequences. We found that fish were reliably recruited by the mobile dummy if it emitted electrical signals and followed it largely independently of the presented playback patterns. While following the dummy, fish interacted with it spatially by displaying stereotypical motor patterns, as well as electrically, e.g. through discharge regularizations and by synchronizing their own discharge activity to the playback. However, the overall emission frequencies of the dummy were not adopted by the following fish. Instead, social signals based on different temporal patterns were emitted depending on the type of playback. In particular, double pulses were displayed in response to electrical signaling of the dummy and their expression was positively correlated with an animals' rank in the dominance hierarchy. Based on additional analysis of swimming trajectories and stereotypical locomotor behavior patterns, we conclude that the reception and emission of electrical communication signals play a crucial role in mediating social interactions in mormyrid weakly electric fish.
Highlights
Communication is an integral component in coordinating interactions between individuals, spanning a wide range of social contexts from agonistic behavior to the formation of groups and collective decision making [1, 2]
Active electrolocation is based on the perception of these self-generated signals through mormyromast electroreceptor organs [8, 9], which are specialized for detecting object evoked amplitude and waveform modulations of the local electric organ discharges (EOD) and are distributed over large areas of the animals’ skin [10, 11]
Our results provide new insights into the relationship between motor behaviors and electric signaling strategies in weakly electric fish
Summary
Communication is an integral component in coordinating interactions between individuals, spanning a wide range of social contexts from agonistic behavior to the formation of groups and collective decision making [1, 2]. Mormyrid weakly electric fish have evolved a unique electro-sensory capability: by emitting pulse-type electric organ discharges (EOD) they use the same signals both for actively probing their environment, i.e. active electrolocation [6], and for communication with conspecifics [7]. Active electrolocation is based on the perception of these self-generated signals through mormyromast electroreceptor organs [8, 9], which are specialized for detecting object evoked amplitude and waveform modulations of the local EODs and are distributed over large areas of the animals’ skin [10, 11]. Electrocommunication is mediated by a different type of electroreceptor organ, the so called knollenorgans [12], which are time-coders that respond very sensitively to the EODs of other electric fish. The inter-discharge intervals (IDI) are highly variable in duration and their temporal sequence can be related to an animal’s current behavioral state [18]
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