Many organisms that lack vision rely on chemical signals to glean information from their environment. Little is known, however, about the ability of sea urchins to detect and respond to such signals. This lack of understanding is especially surprising given the ecological impact of urchins in their respective communities. Regardless of geography, urchins exert strong top down control of plants, algae, and sedentary invertebrates, and these effects are especially evident when urchins, or urchin predators, are removed from an ecosystem. Facultative omnivorous species such as Lytechinus variegatus may greatly alter the abundances of other invertebrates in seagrass communities by preying on juvenile and adult bivalves as well as gastropod egg masses. These potential food resources, however, are patchily distributed within seagrass beds. To find such resources before other organisms can exploit them may require acute abilities to detect signals emanating from these patches. Experiments performed in this study demonstrated a consistent ability of L. variegatus to detect and orient to chemicals emanating from potential food resources over a distance of 1 m. Unlike what has been found in some other marine organisms, turbulent flow conditions did not negatively affect the ability of L. variegatus to find the source of this chemical cue. In fact, only the slowest flows hindered this ability; the bluff shape of the urchin formed a relatively large boundary layer at slow flows, preventing the delivery of chemical signals to the sensors. The relatively high success rates of L. variegatus in turbulent flows may allow it to effectively forage in areas where other organisms cannot. Thus, turbulence may provide a selective advantage for this animal, based on its comparative ability to detect and respond to signals in its environment.

The mechanism behind magnetoreception – the ability to sense magnetic fields for orientation and navigation – still remains one of the most difficult questions to answer in sensory biology, with fish being just one of many taxa known to possess this sense. Characterizing a magnetic sense in fish is crucial for understanding how they navigate their environment and can inform on how increasing anthropogenic sources of electromagnetic fields in aquatic environments may affect threatened fish species. This study examined the hypothesis put forth by Natan and Vortman (2017) that magnetotactic bacteria (MTB), bacteria that create their own chains of magnetic particles for navigational use, act in symbiosis with their animal host to convey magnetic information about their surroundings. Utilizing existing, publicly available datasets of raw genomic sequences, this study demonstrated the presence of MTB within a diverse array of fishes and identified differences in species diversity of MTB between freshwater and marine species of fish. Future research aimed at identifying MTB in specific fish tissues, such as the eye and other neural tissues, will be necessary to provide support for this hypothesis and to further examine the relationships that MTB may have with magnetically sensitive animals.

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.

Irritable Bowel Syndrome (IBS) is one of the most common functional disorders of the gastrointestinal tract. Visceral hypersensitivity is the most commonly reported symptom of IBS, yet is the least adequately treated. Mechanosensitive information from the colon is relayed to the CNS by extrinsic colonic primary afferent nerves which have their cell bodies within dorsal root ganglia (DRG). This thesis aims to identify the contribution of several putatively mechanosensitive ion channels (ASIC1, 2 and 3, TRPV4 and TRPA1) toward detection of mechanical stimuli in the colon. This involvement is assessed by both molecular and functional means. The abundance of each of these channels was assessed by comparing expression within whole DRG against that in specifically colonic DRG neurons using an in situ hybridization methodology developed as part of this PhD. The functional role TRPV4 and TRPA1 impart toward colonic mechanosensation was investigated by recording responses to mechanical stimuli from colonic primary afferent fibres and comparing the results from mice genetically modified to lack either TRPV4 or TRPA1 with those of their intact littermates. The results from these studies indicate expression patterns within whole DRG do not provide accurate representation of the organ of interest, with abundances of each of the channels investigated differing between colonic DRG cells and the whole DRG. In particular ASIC3 and TRPV4 are preferentially expressed in colonic DRG neurons, unlike ASIC2 and TRPA1. Further, TRPV4 is functionally restricted to detection of noxious mechanical stimuli in the colon, while expression of TRPA1 is more widespread and functionally less restricted. Each of these channels are each potential targets for the treatment of IBS as each affects specific aspects of colonic mechanotransduction. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1347202 / Thesis (Ph.D.) - University of Adelaide, School of Molecular and Biomedical Sciences, 2008

Le système nerveux somatosensoriel permet l'interaction entre l'organisme et son environnement. Ce système collecte, via des récepteurs périphériques, les stimuli extérieurs et les transmet au système nerveux central par les neurones sensoriels primaires, dont les corps cellulaires sont situés dans les ganglions rachidiens dorsaux. Ces neurones primaires sont spécifiques des différentes sensations et ont, pour y répondre, des récepteurs, des modalités sensorielles, des caractéristiques moléculaires différentes. Ils sont généralement séparés en 3 grandes familles: les propriocepteurs, les mécanocepteurs et les nocicepteurs, chacune de ces familles se séparant à son tour en une multitude de sous familles. Ces neurones dérivent de la crête neurale, une structure spécifique des vertébrés. Au cours de leur migration vers les ganglions rachidiens dorsaux, les cellules vont être soumises à un grand nombre de facteurs et de voies de signalisation, qui vont entrainer leur survie, leur mort ou leur différenciation. Le facteur de transcription Meis2 a été isolé par l'équipe comme un candidat pouvant intervenir dans cette différentiation des cellules en neurones différenciés. Chez les souris, son expression est spécifique de sous populations mécanoceptives et proprioceptives, et s'étend des stades précoces de développement jusqu'à l'âge adulte. La lignée conditionnelle de souris Knock Out pour Meis2, croisée avec la lignée Wnt1cre, permet l'abolition de Meis2 dans toutes les cellules de la crête neurale et ses dérivés. Le mutant issu de ce croisement meurt à la naissance, avec de nombreux problèmes phénotypiques. Cette lignée cKOMeis2 a alors été croisée avec la lignée Islet1cre, ce qui permet d'invalider le gène Meis2 dans les neurones post-mitotiques des ganglions rachidiens dorsaux. Cette souris m'a servi de modèle afin de déterminer les conséquences éventuelles de la perte de Meis2 dans les neurones sensoriels du ganglion rachidien dorsal par analyse comportementale. / The somatosensory nervous system allows the interaction between the organism and the environment. This system receives from peripheral receptors some exterior stimuli which are transmitted to the central nervous system by sensory primary neurons. Their cell bodies are located in the dorsal root ganglions (DRG). These primary neurons are specific to various sensations and are characterized by specific receptors, sensory modalities and molecular characteristics involved in their response. They are usually defined as belonging to one of three main families: proprioceptors, mecanoceptors and nociceptors, and each family is composed of a large number of subgroups. These neurons are derived from the neural crest cells to form the DRG. The cells are exposed to a number of key pathways and factors, which permit their survival, death or differentiation. The transcription factor Meis2 was isolated by our team as a good candidate to act in the differentiation or specification of these cells into sensory neurons. The expression pattern of Meis2 is shown to be specific to the mecanoceptor and proprioceptor subgroups and starts, in mice, from the early stages of development up to the adult age. To investigate the role of Meis2 the conditional strain mice Meis2 Knock Out (cKOMeis2) were crossed with the strain Wnt1cre which invalidates the gene Meis2 in all the neural crest and derived cells. The new born mice die at birth with most showing phenotypic dysfunctions. Finally, this cKOMeis2 strain was crossed with Islet1cre which specifically disrupts the Meis2 gene in post-mitotic DRG neurons. This thesis characterises the Islet1cre/+cKOMeis2LoxP/LoxP strain in order to determine the behavioural consequences of the loss of the Meis2 protein in DRG sensory neurons.

Chemosensation is achieved through the binding of chemical signals to chemoreceptor proteins embedded in the membranes of sensory neurons. The molecular identity of these receptors, as well as the downstream processing of chemosensory signals, has been well studied in arthropods and vertebrates. However, very little is known about molluscan chemosensation. The identity of chemoreceptor proteins in the nudibranch mollusc Berghia stephanieae are unknown. Data from other protostome and molluscan studies suggest Berghia may use ionotropic receptors for some forms of chemoreception. This study used a bioinformatics approach to identify potential chemosensory ionotropic receptors in the transcriptome of Berghia. A hidden Markov model program was used to generate molecular profiles of previously identified chemosensory receptors in other animals. A Berghia transcriptome was then searched for likely homologous sequences. Candidate sequences were investigated using protein prediction tools and molecular phylogenies. Fourteen ionotropic glutamate receptors (likely synaptic) and five divergent ionotropic receptors were identified. One of these divergent ionotropic receptor sequences, IR-D, may encode a chemosensory receptor and was therefore selected to determine its cellular expression in sensory and brain tissue using in situ hybridization chain reaction. Expression was seen in the rhinophores and oral tentacles of Berghia, as well as in the rhinophore ganglion, cerebral-pleural ganglion, and pedal ganglion. Similar expression patterns were obtained with tissue-specific transcriptomic data. This was the first study to investigate IR-D as a potential chemosensory receptor in molluscs, and thus has helped identify a new family of possible ionotropic chemoreceptor proteins in molluscs. These results have laid the groundwork for continued investigation of Berghia’s chemosensory system.