Meeting Abstract
The blind Mexican cavefish, Astyanax mexicanus, is a natural model system for regressive evolutionary change. These fish have evolved various extreme morphologies as a consequence of life in total darkness. Adult cavefish exhibit cranial aberrations that impact the bones encircling the collapsed eye orbit. These dermal bones demonstrate fragmentation marked by the incomplete fusion of multiple smaller bony pieces. This contrasts with the single bones present in the extant surface morphotype. Yamamoto et. al. (2003) showed that juveniles of both morphotypes develop from a single condensation of mesenchymal cells, i.e., the primary ossification center. In surface fish, this center expands into an intact third suborbital (SO3) bone. In cavefish, however, they observed multiple secondary ossification centers that form, based on analyses of fixative-preserved specimens. To understand the developmental basis of facial bone fragmentation, we performed an intra-individual live-staining procedure involving the bone-specific stain, Calcein. This enabled us to document dynamic features of bone growth and reabsorption. We quantified differences in the size (area growth over time), shape, and presence/absence of ossification centers within individual cavefish. This work reveals dynamic changes to the cranial complex in cavefish over the course of their development, and provides the opportunity to better understand the precise molecular, genetic and developmental features underlying these cranial abnormalities.
