engleski

Understanding the colonization of caves: Effects of constant darkness on the surface form of Astyanax mexicanus

The fish Astyanax mexicanus is able to survive in sunlight as well in the depths of caves concealed in complete darkness. Those living in light are called surface fish and those in the dark are called cavefish. However, on occasion surface fish have been encountered living in caves, and the cavefish are descended from surface fish ancestors that originally colonized caves. It is not clear what adaptations the surface fish colonizers had to make in order for their progeny to survive in complete darkness for many generations and eventually evolve into cavefish. The purpose of this research is to understand the effects of darkness on surface fish by studying a suite of dark-related physiological traits and changes on a molecular level. The study groups were surface fish born at the same time and raised separately for 6 months, one-half kept in completely dark conditions and the other half kept in normal 14-hour light/10-hour dark conditions. All other factors were kept identical between the two groups of fish. Our results showed that darkness had an effect on the expression of genes involved in the hypothalamic-pituitary-adrenal (HPA) axis, which controls basal and stress- related homeostasis and energy storage and expenditure. Furthermore, our research has shown that darkness causes increased stress measured by cortisol levels. Future investigations will be conducted to determine if any other physiological and molecular differences occur between the two groups of fish using a genome wide approach. The results suggest that neuroendocrine changes in the HPA axis related to stress and energy budgeting may be one of the early physiological effects of constant darkness on the surface form of Astyanax mexicanus.

cavefish ; adaptation to darkness ; cave colonization ; stress

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