Meeting Abstract
Astyanax mexicanus cavefish have undergone dramatic morphological changes, relative to their closely-related surface-dwelling relatives, including the loss of eyes and pigmentation. Adult cavefish also harbor cranial malformations, particularly in the suborbital series of bones surrounding the collapsed eye orbit. For example, in cavefish the third and largest suborbital bone (SO3) is fragmented into as many as 10 distinct bony elements. To shed light on the developmental basis of SO3 fragmentation, we performed a longitudinal, intra-individual staining and visualization procedure in live fish. We compared normal SO3 bone growth in surface fish with aberrant growth in cavefish from the onset of ossification through mature bone development. Surface fish SO3 bones form from a single ossification center directly inferior to the eye that expanded uniformly in an antero-posterior direction. In contrast, cavefish demonstrated multiple, secondary ossification centers arising spontaneously throughout development. Some of the ectopic ossification centers resulted in distinct fragments, but less frequently (~13% of the time) they were resorbed into the larger bony element. Interestingly, in cavefish a later post-ossification remodeling mechanism (mediated by osteoclast activity) led to the appearance of “channels” in the bony matrix resulting in fragmented bones. This second mechanism accounted for 90% of fragmented SO3 bones in cavefish. In sum, surface fish display typical patterns of SO3 bone growth, while two distinct ossification processes underlie fragmentation in cavefish. This work reveals dynamic changes to the cranial complex in cavefish, which arose in response to the extreme pressures of the cave environment.
