Subterranean Fishes of the World

3247

2017

AIM 2017

Evolving animals shift their sensory systems to acquire environmental information and express adaptive behaviors. However, the evolutionary mechanism of its integration into the brain is largely unknown. Astyanax mexicanus includes eyed surface populations (surface fish) and isolated populations living in caves (cavefish). Cavefish evolved from surface fish ancestors millions years ago and quickly adapted to their new environment by acquiring specific traits such as eye loss and albinism. A significantly enhanced trait, Vibration Attraction Behavior (VAB) – ability to swim towards prey in darkness – is found in cavefish making this Mexican tetra a unique model for sensory evolution. The superficial neuromasts (SN) present at the eye orbit are the mechanosensory units responsible for VAB. Since SN, covered by mucus cupula, are scattered on entire skin surface, neuromasts can have distinct sensing properties based on their position. Here, we present the millisecond resolution recording of the cupula movements using fluorescent microspheres. The phase-locked movement of cupula we observed suggest that these could stimulate SN neurons in applied frequency. We are then testing whether this mechanical property of cupula differs depending on the cranial areas in different cave populations. We are also testing how stable the neuromast development is in surface fish and cavefish and the difference in the neural wirings. The pharmacological inhibition of Endothelin signaling induced more neuromasts in the cranial region of cavefish than in surface fish, suggesting that cavefish lost ‘safety-lock’ stabilizing the number of SN. In addition, neuromast enhanced-cavefish did not increase VAB, suggesting an additional factor to establish high-level VAB. We are also generating a brain atlas for both morphs and mapping neural wirings of the cranial lateral line system. Above all, we are underway to reveal the evolutionary mechanism of the specialized eye orbit-SN and its impact on VAB.

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