Subterranean Fishes of the World

6218

2023

Pitzer Senior Theses. 138. This Open Access Senior Thesis is brought to you for free and open access by the Pitzer Student Scholarship at Scholarship@Claremont. It has been accepted for inclusion in Pitzer Senior Theses by an authorized administrator

The Astyanax mexicanus is a single species of fish that has two very distinct morphs, the cave fish and the surface fish. 200,000 years ago, cave fish ancestors entered the dark and challenging cave environment of Mexico and were forced to adapt in order to survive. Such adaptions include larger fat reserves, more sensitive olfaction, increased neuromasts, and a unique nervous system structure. Yet, other functions regressed, as they lost their eyes and pigmentation. The Duboué lab has established a clear reciprocal relationship between the volume of structures involved in the neuronal adaptations, but the biological mechanisms underlying the development of these traits are still unknown. Altered distribution of proliferative, or replicating, cells early in development might be contributing to the unique neuroanatomy of each morph. We predicted that proliferating cells destined for the optic tectum in surface fish are instead redirected to the hypothalamus in cave fish. By modifying a technique typically used for isolated cell culture, called EdU (5-Ethynyl-2’-deoxyuridine) immunostaining, we aimed to detect proliferative cells in the Astyanax model system. In the embryonic stage of development, EdU was incorporated into the DNA of proliferative cells, then at 6 days post fertilization, cells expressing EdU in their DNA were stained with Alexa fluor dye to reveal their location. The protocol was successful, and preliminary data showed increased optic proliferation in surface fish, supporting the hypothesis. Observing the translocation of proliferative cells in cave fish and surface fish has allowed for clarification into the mechanisms of neuroanatomic evolution that can in turn be used to inform general models of how animal brains evolve to ever changing external conditions.

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