Chapter 12 – Neural Development and Evolution in Astyanax mexicanus: Comparing Cavefish and Surface Fish Brains

Astyanax cavefish are fascinating animals that have survived in the dark over evolutionary times. Beyond their spectacular loss of eyes, their nervous system has undergone many significant changes that affect their behavior. Here, we review current knowledge on the early embryonic and larval mechanisms underlying developmental evolution of the cavefish brain and sensory systems, and which mainly lead to subtle variations in the size of brain regions or in the number of neurons. We also review recent data showing major modifications of brain neurochemistry in cavefish, which are due to mutations in genes controlling neuromodulatory transmitter balance. Globally, a picture emerges to start explaining the developmental and molecular mechanisms of cavefish behavioral adaptation.