Neural Crest Transplantation Reveals Key Roles in the Evolution of Cavefish Development

Evolutionary changes in Astyanax mexicanus cavefish with respect to conspecific surface fish, including the regression of eyes, loss of pigmentation, and modification of the cranial skeleton, involve derivatives of the neural crest. However, the role of neural crest cells in cavefish evolution and development is poorly understood. One of the reasons is that experimental methods for neural crest analysis are not well developed in the Astyanax system. Here we describe neural crest transplantation between Astyanax surface fish and cavefish embryos. We found differences in the migration of cranial neural crest cells transplanted from the surface fish anterior hindbrain to the same region of surface fish or cavefish hosts. Cranial neural crest cells migrated extensively throughout the head, and to a lesser extent the trunk, in surface fish hosts but their migration was mostly restricted to the anterior and dorsal head regions in cavefish hosts. Cranial neural crest cells derived from the surface fish transplants invaded the degenerating eyes of cavefish hosts, resulting in increased eye size and suggesting that cavefish neural crest cells are defective in forming optic derivatives. We found that melanophores were formed in albino cavefish from grafts of surface fish trunk neural crest cells, showing that the cavefish tissue environment is conducive for pigment cell development, and implicating intrinsic changes in cavefish neural crest cells in loss of body pigmentation. It is concluded that changes in neural crest cells play key roles in the evolution of cavefish development.