Waveform discrimination in a pair of pulse‐generating electric fishes

2020

Self Cite

Understanding how individuals detect and recognize signals emitted by conspecifics is fundamental to discussions of animal communication. The species pair Gymnotus omarorum and Brachyhypopomus gauderio, found in syntopy in Uruguay, emit species-specific electric organ discharge (EOD) that can be sensed by both species. The aim of this study was to unveil whether either of these species is able to identify a conspecific EOD, and to investigate distinctive recognition signal features. We designed a forced-choice experiment using a natural behavior (i.e. tracking electric field lines towards their source) in which each fish had to choose between a conspecific and a heterospecific electric field. We found a clear pattern of preference for a conspecific waveform even when pulses were played within 1 Hz of the same rate. By manipulating the time course of the explored signals, we found that the signal features for preference between conspecific and heterospecific waveforms were embedded in the time course of the signals. This study provides evidence that pulse Gymnotiformes can recognize a conspecific exclusively through species-specific electrosensory signals. It also suggests that the key signal features for species differentiation are probably encoded by burst coder electroreceptors. Given these results, and because receptors are sharply tuned to amplitude spectra and also tuned to phase spectra, we extend the electric color hypothesis used in the evaluation of objects to apply to communication signals.

Section: Introductionmentioning

confidence: 91%

Section: General Experimental Designmentioning

confidence: 99%

Electrocommunication in pulse Gymnotiformes: the role of EOD time course in species identification.

Waddell

2020

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The captivating effect of electric organ discharges: species, sex and orientation are embedded in every single received image

Waddell

2021

Some fish communicate using pulsatile, stereotyped electric organ discharges (EODs) that exhibit species- and sex-specific time courses. To ensure reproductive success, they must be able to discriminate conspecifics from sympatric species in the muddy waters they inhabit. We have previously shown that they use the electric field lines as a tracking guide to approach conspecifics (electrotaxis) in both Gymnotus and Brachyhypopomus genera. Here we show that the social species Brachyhypopomus gauderio uses electrotaxis to arrive abreast a conspecific, coming from behind. Stimulus image analysis shows that, even in a uniform field, every single EOD causes an image in which the gradient and the local field time courses contain enough information to allow the fish to evaluate conspecific sex, and to find the path to reach it. Using a forced-choice test we show that sexually mature individuals orient themselves along a uniform field in the direction encoded by the time course characteristic of the opposite sex. This indicates that these fish use the stimulus image profile as a spatial guidance clue to find a mate. Embedding species, sex, and orientation cues is a particular example of how species can encode multiple messages in the same self-generated communication signal carrier, allowing for other signal parameters (e.g., EOD timing) to carry additional, often circumstantial, messages. This ‘multiple messages’ EOD embedding approach expressed in this species is likely to be a common and successful strategy widespread across evolutionary lineages and among varied signaling modalities.

The sensory effects of light on the electric organ discharge rate of Gymnotus omarorum

Camargo

Aguilera

2023

Gymnotiformes are nocturnal fishes inhabiting the root mats of floating plants. They use their electric organ discharge (EOD) to explore the environment and to communicate. Here we show and describe tonic and phasic sensory-electromotor responses to light distinct from indirect effects depending on the light-induced endogenous circadian rhythm. At dark, principally during the night, inter-EOD interval histograms are bimodal, the main peak corresponds to the basal rate and a secondary peak corresponds to high frequency bouts. Light caused a twofold tonic but opposed effect on the EOD histogram: a) decreased the main mode and b) blocked the high frequency bouts and consequently increased the main peak at the expense of an erasure of the secondary one. Additionally, light evokes phasic responses whose amplitude increases with intensity but whose slow time course and poor adaptation differentiate from the so-called novelty responses evoked by abrupt changes in sensory stimuli of other modalities. We confirmed that Gymnotus omarorum tends to escape from light suggesting that these phasic responses are probably part of a global “light avoidance response”. We interpret the data within an ecological context. Fish rest under the shade of aquatic plants during the day and light spots due to the sun's relative movement alerts the fish to hide in shady zones to avoid macroptic predators and facilitate tracking the movement of floating plant islands by wind and/or water currents.