Underwater robots equipped with artificial electric sense for the exploration of unconventional aquatic niches

International audienceThis article presents different use of the electric field perception in the context of underwater robot navigation. To illustrate the developed navigation behaviours we will introduce a recently launched european project named subCULTron and will show some simulation and experimentation results. The project sub- CULTron aims at achieving long-term collective robot exploration and monitoring of underwater environments. The demonstration will take place in the lagoon of Venice, a large shallow embayment composed of salt turbib water that represents a challenging environment for underwater robots as common sensor like vision or acoustic are difficult to handle. To overcome turbidity and confinement problems our robots will be equipped with artificial electric sensors that will be used as the main sensorial modality for navigation. Electric sense is a bio-inspired sense that has been developed by several species of fish living in turbib and confined underwater environment. In this paper, many different robotic behaviours based on the electric field perception will be presented, in particular we will address reactive navigation, object/robots detection, and object localization and estimation

Active Electric Imaging: Body-Object Interplay and Object's “Electric Texture”

This article deals with the role of fish's body and object's geometry on determining the image spatial shape in pulse Gymnotiforms. This problem was explored by measuring local electric fields along a line on the skin in the presence and absence of objects. We depicted object's electric images at different regions of the electrosensory mosaic, paying particular attention to the perioral region where a fovea has been described. When sensory surface curvature increases relative to the object's curvature, the image details depending on object's shape are blurred and finally disappear. The remaining effect of the object on the stimulus profile depends on the strength of its global polarization. This depends on the length of the object's axis aligned with the field, in turn depending on fish body geometry. Thus, fish's body and self-generated electric field geometries are embodied in this “global effect” of the object. The presence of edges or local changes in impedance at the nearest surface of closely located objects adds peaks to the image profiles (“local effect” or “object's electric texture”). It is concluded that two cues for object recognition may be used by active electroreceptive animals: global effects (informing on object's dimension along the field lines, conductance, and position) and local effects (informing on object's surface). Since the field has fish's centered coordinates, and electrosensory fovea is used for exploration of surfaces, fish fine movements are essential to perform electric perception. We conclude that fish may explore adjacent objects combining active movements and electrogenesis to represent them using electrosensory information

Species-Specific Diversity of a Fixed Motor Pattern: The Electric Organ Discharge of Gymnotus

Understanding fixed motor pattern diversity across related species provides a window for exploring the evolution of their underlying neural mechanisms. The electric organ discharges of weakly electric fishes offer several advantages as paradigmatic models for investigating how a neural decision is transformed into a spatiotemporal pattern of action. Here, we compared the far fields, the near fields and the electromotive force patterns generated by three species of the pulse generating New World gymnotiform genus Gymnotus. We found a common pattern in electromotive force, with the far field and near field diversity determined by variations in amplitude, duration, and the degree of synchronization of the different components of the electric organ discharges. While the rostral regions of the three species generate similar profiles of electromotive force and local fields, most of the species-specific differences are generated in the main body and tail regions of the fish. This causes that the waveform of the field is highly site dependant in all the studied species. These findings support a hypothesis of the relative separation of the electrolocation and communication carriers. The presence of early head negative waves in the rostral region, a species-dependent early positive wave at the caudal region, and the different relationship between the late negative peak and the main positive peak suggest three points of lability in the evolution of the electrogenic system: a) the variously timed neuronal inputs to different groups of electrocytes; b) the appearance of both rostrally and caudally innervated electrocytes, and c) changes in the responsiveness of the electrocyte membrane

The EOD Sound Response in Weakly Electric Fish

1. A spontaneous EOD response to sound is described in two gymnotoids of the pulse Electric Organ Discharge (EOD) type, Hypopomus and Gymnotus, and in one mormyrid, Brienomyrus (Figs. 2-4). 2. In all three species, the EOD response to the sound onset was a transient EOD rate increase. In the low EOD rate Hypopomus (3-6 EODs/s at rest) the first, second, or third EOD interval following sound onset was significantly shorter than the average EOD interval before stimulation. The shortest latency found was 100 ms, the longest ca. 1.2 s. Gymnotus (around 50 EODs/s at rest) responded similarly, but the third interval after sound onset was the first to be affected even at highest intensities (shortest latencies approx. 60 ms; latencies >0.5 s at low sound intensities). In Brienomyrus (4-8 EODs/s at rest) the response occurred already at the first EOD interval after sound onset. 3. An EOD sound response was recorded in Hypoporous and in Gymnotus up to 5,000 Hz sound frequency (in one Gymnotus individual: up to 7,000 Hz). Due to technical limitations the low frequency limit of the response could not be exactly determined: the fishes responded well even below 100 Hz. Hypopomus had its maximum sensitivity around 500 Hz (Fig. 5), Gymnotus around 1,000 Hz (Fig. 6). 4. In all three species the EOD sound response was graded with sound intensity (Hypopomus: Fig. 7). 5. No EOD response to sound was found in two gymnotoids of the wave type, Eigenmannia and Apteronotus, and in the gymnotoid pulse fish Rhamphichthys. A criterion is proposed by which it should be possible to predict whether or not a weakly electric fish species will show the EOD sound response. 6. It is concluded that the EOD response to sound is similar to EOD responses to other kinds of stimulation (light, touch, vibration, food, and even electrical). The possible biological function is discussed

Electric signalling and reproductive behaviour in a mormyrid fish, the bulldog Marcusenius macrolepidotus (South African form)

Bulldog fish (Marcusenius macrolepidotus) generate short (<1 ms) electric-organ discharges (EODs), separated by much longer and highly variable interdischarge intervals (IDIs). We observed overt behaviour and electrical activity during reproductive behaviour in a male and in a female bulldog, and identified IDI patterns with putative signal functions. In contrast to Pollimyrus adspersus and Pollimyrus isidori, in which an elaborate and extended courtship precedes spawning proper, our fish started spawning almost immediately when we allowed the female to enter the male’s territory. The male did not construct a nest, and neither parent provided parental care. The male showed very little aggression towards the intruding female. Fish spawned in bouts near the male’s hiding place, and eggs were scattered by the female’s vigorous tail flips as she left the spawning site, only to return shortly thereafter. During spawning bouts, both fish generated highly stereotyped IDI patterns: the male generated a series of IDIs gradually decreasing from about 200 ms to about 55 ms that was abruptly terminated by a long IDI. The female generated a series of relatively regular IDIs (about 54 ms) that was followed by a marked increase in IDI duration (the probable time of spawning). Finally, a sharp decrease in IDIs to about 20 ms accompanied the female’s sudden escape from the spawning site. In between spawning bouts, both fish generated series of very short IDIs (high discharge rate, HD) that alternated abruptly with very low-rate inter-HD activity (especially in the male). IDIs as short as 9 ms (male) or 11 ms (female) occurred during HD displays. No visible aggression, in fact very little overt behaviour, occurred during these HD displays in both fish. Agonistic interactions between male and female, outside a reproductive context, were similar to those previously described in male pairs, including overt behavioural patterns such as parallel swimming, antiparallel display and attack, as well as HD displays. When not interacting, fish did not generate HD displays. We suggest the HD display is a communication signal in both reproductive and agonistic contexts