Subterranean Fishes of the World

4399

2019

84 pages

University of Cincinnati, Arts and Sciences: Biological Sciences

84 pages

This thesis examines the role of light in global RNA architecture. To accomplish this, the blind Mexican cavefish, Astyanax mexicanus, has been reared in total darkness for ~5 years. This species, which encompasses both river-dwelling and cave-dwelling morphotypes, is notable for the dramatically different phenotypes apparent in each of these morphotypes. The cavefish, in contrast to surface fish, exhibits a dramatic reduction of eyes and pigmentation in addition to an expansion of non-visual sensory systems, amongst other traits. Additionally, lighting conditions experienced by the cave and surface populations of fish differ dramatically between the extreme darkness of the cave and the diurnal light cycle of surface waters. This project has examined the effect of light on gene expression by investigating differential expression seen when a cavefish is restored to “Natural Conditions”—a comparative paradigm of lighting condition encompassing total darkness for cavefish and a diurnal light/dark cycle for surface fish. By examining the role of light in gene expression in this system, it expands the paradigm of how surface fish were able to successfully colonize the cave environment. Global gene expression is least similar under Natural Conditions by correlative comparison, and the number of genes differentially expressed between the two morphotypes is greatly expanded. This expansion of differentially expressed genes represents a subset of expression that is likely inducible by dark lighting conditions. The functional repertoire of this gene set implicates the circulatory and olfactory systems as potential down-stream targets of light-affected gene expression. Additional comparisons of gene expression were made at locations of QTL markers which have been implicated in eye or pigmentation reduction in the cavefish compared to the surface fish. Comparisons between cave and surface fish reared on Light/Dark Conditions are not the same as comparisons conducted on Natural (photic) Conditions when examined both globally and functionally. This comparison provides a greater understanding of how these inherently regressive traits may have been lost in the dark environment, identifying novel candidate genes mediating eye or pigmentation loss. In sum, examining the effect of light on gene expression in this system grants a better understanding of the complex genetic architecture accompanying life in the extreme cave environment. This study illuminates the need to understand the effect that rearing under light and non-natural conditions has on animals whose natural environment is one of total darkness.

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