Sensory biology of animals is studied throughout the world for the insight it provides to understanding ecosystems and improving how we manage species. In this research, I designed experiments to investigate the sensory biology and behaviour of two Australian species of freshwater crayfish from the genus Cherax, the yabby (Cherax destructor) and redclaw crayfish (Cherax quadricarinatus). Experimental apparatus were constructed and tailored to test specific questions on physiology, tactile (touch) sensitivity, observation techniques, aggressive behaviour and responses to electrical fields. The outcomes were: / • abdominal muscle mass was positively correlated to the size of the electrical fields produced by swimming crayfish, / • behaviour changed in response to contact with different structures and textures of wall surfaces, / • computer analysis of underwater behaviour was similar to that scored by a human observer, / • the level of aggression in groups of crayfish changed as group size increased, and / • two species of crayfish responded to electrical fields in the water by decreasing their locomotory movement. / These results reveal a way in which physiology relates to behaviour, how crayfish and other crustaceans may sense the invisible and behave in aquaculture ponds, as well as documenting methodology to further investigate these areas in the future.

Elasmobranchs (sharks, skates and rays) possess a sophisticated array of sensory systems that are, undoubtedly, of great importance to their survival. Representing the earliest group of extant jawed vertebrates, detailed study of elasmobranch sensory biology can provide much-needed information on the evolution of vertebrate sensory systems. Some sensory modalities have been studied in detail in several species, but few studies have examined and compared multiple sensory systems within a particular genus. By examining the morphology and physiology of the different sensory systems, correlations can be made within both an ecological and a phylogenetic context. The primary advantage of studying the sensory systems of closely related species is that any differences between them are more likely to reflect functional ecological adaptations rather than the effects of phylogenetic separation. Wobbegongs sharks (Orectolobidae) are a distinctive group of benthic sharks that are characterised by a highly patterned, dorso-ventrally compressed body. Wobbegongs are ambush predators that employ a unique ‘sit and wait’ strategy. Their morphologically distinct body shape, sedentary lifestyle and mode of predation suggest that wobbegong sharks may differ from other elasmobranchs in how they employ their different sensory systems. In this study, four wobbegong species that vary in life-history and/or habitat were examined: the Western wobbegong, Orectolobus hutchinsi, the spotted wobbegong, O. maculatus, the ornate wobbegong, O. ornatus and the dwarf spotted wobbegong, O. parvimaculatus. Vision and olfaction were assessed in all four species. Detailed assessment of electroreception and mechanoreception (lateral line) was conducted only for O. maculatus and O. ornatus. Morphology, physiology and molecular genetics were examined in the visual system, and morphological assessment was conducted for the olfactory, electroreceptive and mechanosensory lateral line systems. The retinae of all four wobbegong species are duplex; rod and cone photoreceptors can be distinguished easily on the basis of morphology. The wavelength of maximum absorbance (λmax) of the rod visual pigment is 496 nm in O. hutchinsi, 484 nm in O. maculatus, 498 nm in O. ornatus and 494 nm in O. parvimaculatus. Absorbance spectra of cone visual pigments were only obtained from O. maculatus and O. ornatus. Only one spectral type of cone was measured in each species, with max values at 553 nm and 560 nm, respectively. Partial sequences were obtained for the rh1 opsin gene in all four species, and for the lws opsin gene in every species except O. parvimaculatus. The apparent presence of only one cone pigment raises the possibility that wobbegongs do not have colour vision. The topographic distribution of cells within the ganglion cell layer of Orectolobus hutchinsi show a weakly elongated central visual streak of increased cell density, mediating a higher spatial resolving power of 2.06 cycles deg-1 in the frontal visual field. Retinal topography of O. maculatus and O. parvimaculatus are similar, with both possessing a dorsal horizontal streak facilitating increased spatial resolving power in the lower visual field. Orectolobus parvimaculatus also possesses an area of increased cell density in the naso-ventral region of the retina mediating acute vision in the upper caudal region of the visual field. Spatial resolving power reaches 3.51 cycles deg-1 and 3.91 cycles deg-1 in O. maculatus and O. parvimaculatus, respectively. The topographical variation in retinal sampling indicates that different regions of the visual field are relatively more important and may reflect interspecific differences in behaviour and habitat. The mean number of lamellae in the olfactory rosette is 47.0 for Orectolobus hutchinsi, 48.7 for O. maculatus, 40.7 for O. ornatus and 55.7 for O. parvimaculatus. Olfactory sensory epithelial surface area is comparable in O. hutchinsi, O. maculatus and O. ornatus, while O. parvimaculatus has a significantly larger surface area, relative to body size, compared to the other three species. Olfaction appears to be relatively more important in O. parvimaculatus, especially during low light conditions, when vision is limited. The distribution of ampullary electroreceptive pores and mechanosensory lateral line pores (pored and non-pored canals) is almost entirely concentrated on the dorsal region of the head in both O. maculatus and O. ornatus. This suggests that both sensory systems are well-adapted and specialised to detect prey swimming overhead when the wobbegong is sitting motionless, thereby facilitating its unique, predatory, “lie-in-wait’ ambush strategy. Orectolobus hutchinsi and O. ornatus appear to be well-suited to both diurnal and nocturnal activities, whereas O. maculatus and O. parvimaculatus are probably most active under low light conditions. Sensory system information inferred from this study correlates well with what is known of the diet and habitat of the four wobbegong species examined. Therefore, in the absence of other biological data, sensory neurobiological approaches can be used to predict such bio-ecological factors as predatory strategy, habitat preference, and behaviour. Electrophysiology and behavioural approaches will provide major advances in future studies in order to understand how each of the different senses is integrated at both peripheral and central levels and how such studies are vital to our understanding of evolutionary and ecological processes.

Multimodal sensory input directs simple and complex behaviors in animals. Most research to date has been limited to studies of individual senses rather than multiple senses working together, leading to important advances in our comprehension of the sensory systems in isolation, but not their complementary and alternative roles in difficult behavioral tasks, such as feeding. In the marine environment, a prey item might emit an odor, create a hydrodynamic disturbance, such as from gill movements or swimming, be visible to the predator, produce a sound, and/or produce a weak electrical field. Therefore, the goal of this study was to investigate the integration of olfaction, mechanoreception by the lateral line system, vision, and electroreception in a marine animal. Sharks were chosen as a model organism in which to investigate multisensory integration because of their sensitivity and acuity, the presence of the same suite of sensory modalities in all species, the availability of experimental animals from different species, habitats and ecologies, and the rich literature on sharks' prey capture behavior. Two approaches were used: controlled artificial stimuli, delivered to the animals, were used to determine the spatial and concentration characteristics of odor encounters that guide the initial orientation to an odor plume in the far field in a model elasmobranch, the smooth dogfish, Mustelus canis; and sensory deprivation was used to restrict the availability of natural cues emanating from live prey items in order to elucidate the complementary and alternating roles of the senses in detecting, tracking, orienting to, striking at, and ultimately capturing prey. In the latter experiments, three species of sharks from different ecological niches were investigated: benthic, suction-feeding nurse sharks (Ginglymostoma cirratum) that hunt nocturnally for fish; ram-biting bonnetheads (Sphyrna tiburo) that scoop crustaceans off the bottom of seagrass beds; and ram-feeding blacktip sharks (Carcharhinus limbatus) that rapidly chase down midwater teleost prey. In orienting to odor patches, bilateral time differences between the nares are more important than concentration differences, such that animals turn toward the side stimulated first, even with delayed pulses of higher concentration. This response would steer the shark into each oncoming odor patch, helping the animal maintain contact with an odor plume. Sensory deprivation experiments revealed similarities and differences among species in terms of which senses they choose to focus on for particular behaviors, likely as a result of differences in the environments that they hunt in, type of prey consumed, and foraging strategies used, as well as anatomical differences in the central nervous system and the sensory organs. In most cases, multiple senses can be used for the same behavioral task. Thus, sharks are capable of successfully capturing prey, even when the optimal sensory cues are unavailable, by switching to alternative sensory modalities, which indicates that feeding behavior is plastic. Nurse sharks rely primarily on olfaction for detection. Olfaction in combination with vision, the lateral line, or touch is required for tracking. Nurse sharks orient to prey using the lateral line, vision, or electroreception, but will not ingest food if olfaction is blocked. Capture is mediated by the electrosensory system or tactile cues. Bonnetheads normally detect prey using olfaction, rely on olfactory-based tracking until they are close to the prey, then vision to line up a strike, and finally electroreception to time the jaw movements for capture. They can detect, orient, and strike visually in the absence of olfactory cues. Blacktip sharks also detect prey using olfaction or vision. Olfaction is used in combination with vision or the lateral line system for tracking. Long-distance orientation and striking is visually mediated, but strike precision relies on lateral line cues and an increase in misses occurs when this system is blocked. In the absence of vision, short-range orientation and striking can occur using lateral line cues. Capture is mediated by electroreception or tactile cues. Collectively, these results were used to develop species-specific sensory hierarchies for shark feeding behavior in a captive environment, the first such hierarchies to cover a complete behavioral sequence in a vertebrate.

L’électro-localisation est le nom donné aux capacités sensorielles de certains poissons électriques, vivant en eaux troubles, capables de détecter les perturbations électrostatiques dues à la présence d’objets dans leurs voisinages. Cette aptitude à interpréter un signal électrique pour se repérer dans l’espace ouvre l’importance perspectives, notamment dans le domaine de la robotique brio-inspiré. Mathématiquement, l’électrolocalisation est proche de la tomographie d’impédance électrique : il s’agit donc d’un problème inverse non linéaire, notoirement mal posé. Nous proposons dans cette thèse d’étudier des méthodes de reconstruction qui permettraient d’obtenir de manière robuste certaines caractéristiques de la forme des obstacles, plutôt que l’ensemble des détails de leurs géométries. Il s’agit donc d’étudier la stabilité de la partie observable des obstacles par rapport à des erreurs dans les mesures. / Electrolocation is the name given to the sensor ability for certain electric fish robots, which are able to detect electrostatic perturbations caused to the presence of some objects in their neighborhood. This ability to interpret an electrical signal to locate itself in space opens important perspectives, including in the field of biologically inspired robotics. Mathematically, electrolocation is linked to the electric impedance tomography: so it’s about a non-linear inverse problem, particularly ill-posed problem. We will, in this Phd, study some methods of reconstruction, which could be obtain robustly some characteristic of the obstacle’s shape, rather all of their geometry details. So, it’s about to study the stability between the observable part of the obstacles and the errors of measurements.

Electroreception is a sensory modality found in some fish, which enables them to sense the environment through the detection of electric fields. Biological experimentation on this ability has built an intricate framework that has identified many of the components involved in electroreception's production, but lack the framework for bringing the details back together into a system-level model of how they operate together. This thesis builds and tests a computational model of the Electrosensory Lateral Line Lobe (ELL) in mormyrid electric fish in an attempt to bring some of electroreception's structural details together to help explain its function. The ELL is a brain region that functions as a primary processing area of electroreception. It acts as an adaptive filter that learns to predict reoccurring stimuli and removes them from its sensory stream, passing only novel inputs to other brain regions for further processing. By creating a model of the ELL, the relevant components which underlie the ELL's functional, electrophysiological patterns can be identified and scientific hypotheses regarding their behavior can be tested. Systems science's approach is adopted to identify the ELL's relevant components and bring them together into a unified conceptual framework. The methodological framework of computational neuroscience is used to create a computational model of this structure of relevant components and to simulate their interactions. Individual activation tendencies of the different included cell types are modeled with dynamical systems equations and are interconnected according to the connectivity of the real ELL. Several of the ELL's input patterns are modeled and incorporated in the model. The computational approach claims that if all of the relevant components of a system are captured and interconnected accurately in a computer program, then when provided with accurate representations of the inputs a simulation should produce functional patterns similar to those of the real system. These simulated patterns generated by the ELL model are compared to recordings from real mormyrid ELLs and their correspondences validate or nullify the model's integrity. By building a computation model that can capture the relevant components of the ELL's structure and through simulation reproduces its function, a systems-level understanding begins to emerge and leads to a description of how the ELL's structure, along with relevant inputs, generate its function. The model can be manipulated more easily than a biological ELL, and allows us to test hypotheses regarding how changes in the structures affect the function, and how different inputs propagate through the structure in a way that produces complex functional patterns.

Electromagnetic fields (EMF) produced by high voltage (HV), submarine transmission cables leading from offshore wind energy generation facilities could affect foraging or migratory behaviors of electro-receptive fishes, including endangered Atlantic Sturgeon. However, no published studies have quantitatively evaluated the possible behavioral effects of EMF exposure on sturgeon during residence in coastal waters. This study evaluated behavioral responses by sub-adult Atlantic Sturgeon to electromagnetic and magnetic fields under controlled laboratory conditions. Fabricated EMF generators were used to emulate a range of field EMF conditions that migratory fishes could encounter in proximity to submarine HV sources. Sensor arrays and digital video recorders synoptically quantified EMF conditions and fish behaviors during experimental trials. This thesis will describe the unique, experimental EMF generator/sensor array, present results of the behavior study, and suggest implications of the findings for Atlantic Sturgeon management and conservation. 45 trials were conducted over the course of the study. Study fish were subjected to 3 different field strengths (5µT, 100 µT, 1000 µT), generated using both AC and DC current. Time spent in generated field area, number of passes through the field area, and swimming speed were used to quantify behavioral changes in test subjects. From the data collected and analyzed there was no evidence indicating a change in fish behavior due to the influence of field strengths, field orientations, or field types used during the study.