EARLY LENS ABLATION CAUSES DRAMATIC LONG TERM EFFECTS ON THE BONES OF THE CRANIOFACIAL SKELETON OF THE MEXICAN TETRA, ASTYANAX MEXICANUS

Abstract

The Mexican tetra, Astyanax mexicanus, exists as two morphs of a single species, a sighted surface morph and a blind cavefish. In addition to eye regression, cavefish have an increased number of taste buds, maxillary teeth and have an altered craniofacial skeleton. I investigated the effect the lens has on the development of the surrounding skull by ablating the lens over early ontogeny. This unique long-term study sheds light on how early embryonic manipulations on the eye can affect the shape of the adult skull. The effects of lens ablation were analyzed using landmark based morphometric analyzes. Morphometric analyzes indicate that there is a significant difference in the shape of the supraorbital bone and suborbital bones four through six. These bones expand into the eye orbit exhibiting variability in their shape. Interestingly, the number of caudal teeth on the lower jaw is also affected by lens ablation. I compared these findings between morphs and across two teleost species. I conducted lens removal in the surface fish to determine if it would produce a cavefish phenotype. Lens removal in the surface fish only partially results in a cavefish phenotype, indicating that lens loss is not solely responsible for the phenotypic differences between the two morphs. The effects of lens removal were then compared in the Mexican tetra and zebrafish. Surprisingly, the results indicate that the same bones are variable in shape in both species, indicating that the variability of these bones is conserved across species. Finally, I compared laser lens damage and full lens removal, to investigate the capacity for both lens regeneration and healing in the Mexican tetra. Together, the lens healing and regeneration studies indicate that lens absence in early development does not influence the shape of the skull. Lens absence during later development influences the mechanical forces in the skull resulting in the bones of the orbital region changing in size and shape. This study highlights the dynamic nature of the skull and sheds light on the influence the eyes (a soft tissue) have on the surrounding skull (a hard tissue) a topic which has been overlooked in the literature.