The lateral line canal system is a sensory organ found in all teleost fish that has a wide range of morphological variation. Variation in morphology may often be the result of evolutionary necessity where the need for function dictates form. Xiphister mucosus is an amphibious Stichaeid fish that inhabits the rocky intertidal zone of the northeastern Pacific Ocean. The rocky intertidal is considered an extreme environment where crashing waves and ebbing tides may require the specialization of adaptations for surviving the many abiotic stressors encountered there. The lateral line trunk canal of Xiphister is regarded as unique among teleosts with multiple, branching, zigzag shaped canals that are morphologically complex. The X. mucosus canal was found to not serve as a mechanosensory organ, rather the findings presented here suggest a new role as a water transport organ. This may be an exaptation to help X. mucosus avoid desiccation during low tides when the fish remain upon the rocky shore and exposed to dehydration. While emersed, Xiphister relies on cutaneous respiration as its primary means of aerial respiration.

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.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 264-277). / The lateral line system on fish has been found to aid in schooling behavior, courtship communication, active and passive hydrodynamic imaging, and prey detection. The most widely used artificial prey stimulus has been the vibrating sphere, which some fish are able to detect even when the signal velocities to its lateral line are orders of magnitude smaller than background current velocities. It is not clear how the fish are able to extract this signal. This thesis uses a series of computational fluid dynamic (CFD) simulations, matched with recent experiments, to quantify the effects of 3D fish body parts on the received dipole signals, and to determine signal detection abilities of the lateral line system in background flow conditions. An approximation is developed for the dipole induced, oscillatory, boundary layer velocity profile over the surface of a fish. An analytic solution is developed for the case when the surface is a wall, and is accurate at points of maximal surface tangential velocity. Results indicate that the flow outside a thin viscous layer remains potential in nature, and that body parts, such as fins, do not significantly affect the received dipole signal in still water conditions. In addition, the canal lateral line system of the sculpin is shown to be over 100 times more sensitive than the superficial lateral line system to high frequency dipole stimuli. Analytical models were developed for the Mottled Sculpin canal and superficial neuromast motions, in response to hydrodynamic signals. When the background flow was laminar, the neuromast motions induced by the stimulus signal at threshold had a spectral peak larger than spectral peaks resulting from the background flow induced motions. / (cont.) When the turbulence level increased, the resulting induced neuromast motions had dominant low frequency oscillations. For fish using the signal encoding mechanisms of phase-locking or spike rate increasing, signal masking should occur. / by Mark Andrew Rapo. / Ph.D.

Per a aquesta tesi, utilitzo la línia lateral del peix zebra com a sistema model per adreçar dues qüestions fonamentals: En una primera línia d’investigació exploro la relació entre la funció d’un òrgan i la seva arquitectura. La regeneració de cèl.lules ciliades a la línia lateral del peix zebra ocorre mitjançant la divisió dels seus progenitors en determinades posicions dins les zones ventral i dorsal del neuromast. Durant la regeneració de les cèl.lules ciliades, es forma una línia de simetria vertical, que bisecciona l’epiteli del neuromast en dues meitats de polaritats planars oposades. La qüestió de com es controla l’anisotropia de la regeneració de les cèl.lules ciliades i com integrar aquest procés en l’establiment de la simetria bilateral d’aquest organ, roman encara per esclarir. En aquest estudi mostro que la simetria bilateral del neuromast es sosté degut a l’activitat compartimentalitzada de Notch qui, permetent l’estabilització dels progenitors de cèl.lules ciliades en compartiments polars específics, organitza l’anisotropia de la regeneració. En una segona línia d’investigació, descric el rol del complex de remodelació de cromatina ATPasa brg1 durant la formació d’organs mecanosensorials al peix zebra. Així mostro que els mutants de brg1 desenvolupen un sistema de linia lateral truncat, donat que brg1 es necessari per a la regulació de múltiples events cel.lulars al primordi de la línia lateral. / In this thesis I use the zebrafish lateral line as a model system to address two fundamental questions. In a first line of investigation I explore the relation between an organ function and its architecture. The regeneration of hair cells in the zebrafish lateral line occurs trough the division of hair-cell progenitors at specific locations in the dorsal and ventral aspects of the neuromasts. As hair cells regenerate a vertical midline that bisects the neuromast epithelium into perfect mirror-symmetric plane-polarized halves is formed. Each half contains hair cells of identical planar orientation but opposite to that of the confronting half. How hair cell regeneration anisotropy is controlled and how this process is integrated in the establishment of this organ bilateral symmetry is poorly understood. Here I show that the neuromast bilateral symmetry is sustained by compartmentalized Notch activity, which governs regeneration anisotropy by permitting the stabilization of hair cell progenitors in specific polar compartments. In a second line of research I report the role of the chromatin remodeling complex ATPase brg1 during mechanosensory organ formation in the zebrafish. I show that brg1 mutants develop a truncated lateral line system as brg1 is needed in the regulation of multiple cellular events in the lateral line primordium.