ABSTRACT
Astyanax mexicanus cavefi sh and their surface dwelling counterparts are a model system for studying the role of development in the evolution of cave related phenotypes. In contrast to many other cave animals, Astyanax is an excellent laboratory organism with frequent and copious spawning and large robust embryos. Here we review molecular, cellular and developmental mechanisms underlying the loss of eyes and pigmentation in Astyanax cavefi sh. Eye degeneration involves enhanced activity of the Hedgehog signaling system along the embryonic midline, which induces lens apoptosis and ultimately causes the arrest of optic growth and changes in craniofacial morphology. The loss of melanophore pigmentation is caused by a specifi c block in the ability of undifferentiated melanoblasts to convert L-tyrosine to L-DOPA, a precursor of melanin. We discuss the importance of a developmental perspective in understanding the evolutionary mechanisms underlying eye and pigment regression.
