Electrosensory Contrast Signals for Interacting Weakly Electric Fish

Abstract

Active sensory systems have evolved to properly encode natural stimuli including those created by conspecifics, yet little is known about the properties of such stimuli. We consider the electrosensory signal at the skin of a fixed weakly electric fish in the presence of a swimming conspecific. The dipole recordings are obtained in parallel with video tracking of the position of the animals. This enables the quantification of the relationships between the recording dipole and the positions of the head, midbody and tail of the freely swimming fish. The contrast of the signal at the skin is shown to be well-fitted by a decreasing exponential function of distance. It is thus anti-correlated with distance; it is also correlated with the second envelope (i.e., the envelope of the envelope) of the raw recorded signal. The variance of the contrast signal is highest at short range. However, the coefficient of variation (CV) of this signal increases with distance. We find a range of position and associated contrast patterns under quasi-2D swimming conditions. This is quantified using global measures of the visit times of the free fish within measurable range, with each visit causing a bump in contrast. The durations of these bumps as well as the times between these bumps are well reproduced by a doubly stochastic process formed by a dichotomous (two-state) noise with Poisson statistics multiplying a colored noise [Ornstein-Uhlenbeck (OU) process]. Certain rapid body movements such as bending or turning are seen to produce contrast drops that may be part of cloaking strategies.

Neural Synchrony Gives Rise to Amplitude- and Duration-Invariant Encoding Consistent With Perception of Natural Communication Stimuli

“…We further hypothesize that the invariant neuronal and behavioral responses to natural electrocommunication stimuli considered here would break down when the stimulus contrast is increased beyond that explored in this study which is experienced when fish are located ∼13 cm from one another (Yu et al, 2019). Indeed, higher contrasts are experienced when two conspecifics move closer (i.e., within 5 cm) to one another (Yu et al, 2012(Yu et al, , 2019, or when the beat frequency is increased. This is because we predict that peripheral afferents will then display stronger phase locking (i.e., only fire during specifics phases) to the background signal, which will increase their synchrony.…”

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

“…For the given situation in the habitat, characterized by a certain water conductivity, electric field compression by the limited water column, and EOD strength, this allowed us to estimate the distance at which the electric field decayed down to the known behavioral sensitivities of several gymnotiform species to approximately 2 m. Within this range fish can detect and perceive each other, as we have shown in the field for attacks of a resident A. rostratus male towards an intruder (Henninger et al, 2018). The boundary effects of the water surface and the bottom, that effectively reduces the exponent of the power law decay (here q = 1.3) of the dipolar electric field (Fotowat et al, 2013;Yu et al, 2019), increase the detection ranges compared to a situation without boundaries and an exponent of two (Knudsen, 1975).…”

“…2 B), the exponent describing the decay of the field amplitude with distance is, with 1.6, clearly smaller than the exponent of 2 of the ideal dipole. The non-conducting bottom of the tank and the water surface induce boundary effects that compress the electric field (Fotowat et al, 2013) and result in a reduced exponent or even an exponential instead of power-law decay (Yu et al, 2019).…”

“…The minute changes induced by nearby objects are much smaller than modulations induced by EODs of con-and allospecific electric fish (Nelson and MacIver, 1999;Chen et al, 2005;Fotowat et al, 2013). By turning and bending the body the field strength and thus detectability at a receiving fish are further reduced even at small distances (Yu et al, 2019). The situation weakly electric fish face resembles walking with a dim flashlight through a forest in the dark: only the immediate environment can be illuminated by the flashlight, but the flashlight of another person can sometimes be seen over a much larger distance.…”

“…7) hints at the complexity of signals gymnotiform fish are actually facing. Most of the behavioral and electrophysiological literature so far has focused on static interactions of two fish, but already relative movements induce higher order amplitude modulations of the resulting signals, so called "envelopes" (Yu et al, 2012(Yu et al, , 2019. The interaction of more than two fish also results in envelopes and in specific behavioral responses (Partridge and Heiligenberg, 1980;Stamper et al, 2012).…”