Abstract

Scleral ossicles are bony elements found along the eyes of many fishes, amphibians, and reptiles. These bones provide a superficial layer of support to the eye and may facilitate visual acuity. Previous research has shown that scleral ossicle diversity is generally limited among teleosts, but that scleral ossicles have been lost numerous times among teleosts inhabiting benthopelagic habitats (Franz-Odendaal, 2008). In this study we further investigate these patterns of intra- and inter-specific variation by examining eyes from multiple individuals of ten riverine teleosts native to Kentucky as well as one population of the Mexican blind cavefish, Astyanax mexicanus, and by re-analyzing a quantitative database of scleral ossicle number and depth preference from over 100 teleosts using newly resolved teleost phylogenies. Consistent with the limited diversity of most teleost families, we find that intraspecific variation in scleral ossiclenumber and size is virtually non-existent among the species sampled, although we do find evidence of additional inter-specific variation among the Cyprinodontiformes, as well as dramatic intra-population variation among cavefish from Chica Cave. Although our data replicates the negative relationship between scleral ossicle number and the depth preference previously found among teleosts (Franz-Odendaal, 2008), even when accounting for phylogenetic relationships, our results further reveal that this relationship is relatively weak. We conclude that further sampling may reveal additional inter- and even intra-specific variation among some groups of teleosts, and that depth could serve as a proxy for other life history traits that more directly influence teleost scleral ossicle diversity such as prey-capture strategies.