Subterranean Fishes of the World

6970

2023

A thesis submitted to the Graduate College of the University of Cincinnati in partial fulfillment of the requirements for the degree of Master of Science in the Department of Biological Sciences of the College of Arts and Sciences

In biology, we often think about systems of the body as isolated anatomies with specific functions. However, systems rarely work in isolation. On the contrary, systems are integrated with one another throughout development. One understudied example of system integration is between the sensory and skeletal systems. The purpose of this study is to explore how the sensory system informs the development and patterning of the skeletal system using the fish lateral line system as a model. It has been shown many times throughout history that the sensory lateral line is integrated with the intramembranous bones of the fish skull through colocalization. Although many hypotheses have been postulated regarding the specifics of this interaction, we do not know the inductive nature between these systems. To further our understanding of these systems, we investigated the sensory canal neuromast organs and suborbital (SO) bones of the Mexican tetra, Astyanax mexicanus. This study is largely based on the model that canal neuromasts induce SO bones. In addition, our model recognizes that neuromast positioning influences the fusion of bone, where close canal neuromasts are associated with fused bones. To investigate the relationship between these two systems, we made comparisons of SO bone patterning between eyeless cave populations and surface fish to understand the impact of eyes on neuromast positioning and bone fusion, conducted genetic analyses such as quantitative trait loci and whole genome sequencing analyses to understand the genetic component of bone fusion, and chemically ablated sensory hair cells to understand their role in bone induction. By comparing fusion patterns across the eyed surface fish and eyeless cave populations, we concluded that the simple absence of an eye is not responsible for SO fusion in iii cavefish. We propose a model where variable eye degeneration in cavefish results in variable canal neuromast positioning, ultimately resulting in variable bone fusion. Through genetic analyses, we found that left SO4/5 bone fusion is mediated by a genetic signal located on Astyanax chromosome 2. We identified a region of interest spanning 4.4Mbp with 121 total genes included in this significant region of the chromosome. Using whole genome sequencing, we found 71 of these genes contain non-synonymous coding sequence changes. Through a candidate gene approach, we also identified 46 genes that are involved in bone, sensory cells, and/or eye development. Finally, we used an ototoxic antibiotic, gentamicin, to ablate sensory hair cells directly before the time of SO ossification. We found that ablating hair cells does not change the timing or initial size of SO bones, suggesting hair cells are not the mediator responsible for SO induction. These results all deepen our understanding of how the lateral line informs the development and positioning of facial bones in the Mexican tetra, supporting the statement that systems of the body do not function in isolation

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