Tracking activity patterns of a multispecies community of gymnotiform weakly electric fish in their neotropical habitat without tagging

Abstract

Field studies on freely behaving animals commonly require tagging and often are focused on single species. Weakly electric fish generate a species-and individual-specific electric organ discharge (EOD) and therefore provide a unique opportunity for individual tracking without tagging. Here, we present and test tracking algorithms based on recordings with submerged electrode arrays. Harmonic structures extracted from power spectra provide fish identity. Localization of fish based on weighted averages of their EOD amplitudes is found to be more robust than fitting a dipole model. We apply these techniques to monitor a community of three species, Apteronotus rostratus, Eigenmannia humboldtii and Sternopygus dariensis, in their natural habitat in Darień, Panama. We found consistent upstream movements after sunset followed by downstream movements in the second half of the night. Extrapolations of these movements and estimates of fish density obtained from additional transect data suggest that some fish cover at least several hundreds of meters of the stream per night. Most fish, including E. humboldtii, were traversing the electrode array solitarily. From in situ measurements of the decay of the EOD amplitude with distance of individual animals, we estimated that fish can detect conspecifics at distances of up to 2 m. Our recordings also emphasize the complexity of natural electrosensory scenes resulting from the interactions of the EODs of different species. Electrode arrays thus provide an unprecedented window into the so-far hidden nocturnal activities of multispecies communities of weakly electric fish at an unmatched level of detail.

Electrocommunication signals indicate motivation to compete during dyadic interactions of an electric fish

“…After computing spectrograms for each channel with fast Fourier transformation (FFT, n fft = 2 15 , corresponds to 1.63 s, 80 % overlap) we first detected peaks in a power spectrum summed over the channels and assigned them to the fundamental EODfs and their harmonics of the two fish. Based on EODfs and the distribution of power in the channels we tracked electric signals over time and obtained EODf traces for each of the two fish (Henninger et al, 2018(Henninger et al, , 2020Madhav et al, 2018).…”

“…Dominance hierarchies have also been suggested for A. leptorhynchus (Hagedorn and Heiligenberg, 1985;Dunlap and Oliveri, 2002). Since behavioral observations suggests A. leptorhynchus to be a solitary living species (Stamper et al, 2010;Raab et al, 2019;Henninger et al, 2020), this dominance can be assumed to be mainly resource based. In appropriate habitats with suitable shelters, A. leptorhynchus is quite abundant, but the fish distribute themselves independently from each other and do not form large social groups (Stamper et al, 2010;Raab et al, 2019, own observations in Colombia 2016.…”

“…Using recently developed techniques for tracking electrocommunication signals in freely behaving electric fish (Henninger et al, 2018; Madhav et al, 2018; Henninger et al, 2020) in addition with infrared video recordings, we recorded electric and physical interactions of pairs of A. leptorhynchus in staged competitions over a superior shelter. Compared to previous studies we significantly expanded the observation times (from ten minutes to six hours) and the number of interacting pairs of fish.…”

“…Already the frequency of their continuous electric organ discharge (EOD) has been suggested to signal an individual's physical condition, dominance status, or aggressiveness (Westby and Box, 1970;Hagedorn and Heiligenberg, 1985;Cuddy et al, 2012). The sexually dimorphic EOD frequency (EODf) of A. leptorhynchus indicates identity and sex (Henninger et al, 2020), with males having higher EODfs than females (Meyer et al, 1987). While some studies also suggest EODf to indicate dominance (Hagedorn and Heiligenberg, 1985;Dunlap and Oliveri, 2002;Cuddy et al, 2012;Henninger et al, 2018;Raab et al, 2019), others were not able to replicate this correlation (Triefenbach and Zakon, 2008).…”

Spooky Interaction at a Distance in Cave and Surface Dwelling Electric Fishes

“…To discover the potential consequences of adaptation for troglobitic life on electrosensory behavior, we compared the electric behavior and movement of the cavefish Eigenmannia vicentespelea to nearby epigean (surface) relatives, Eigenmannia trilineata, that live in the same river system (Figure 1). We used a recently developed approach for characterizing electric behaviors and locomotor movements of weakly electric fishes in their natural habitats (Madhav et al, 2018;Henninger et al, 2020). This approach, which uses a grid of electrodes placed in the water, permits an estimation of features of the electric field of each fish and an analysis of their concurrent movement (Figure 2).…”