Comparative retinal anatomy in four species of elasmobranch
Version of Record online: 24 NOV 2011
Copyright © 2011 Wiley Periodicals, Inc.
Journal of Morphology
Volume 273, Issue 4, pages 423–440, April 2012
How to Cite
Schieber, N. L., Collin, S. P. and Hart, N. S. (2012), Comparative retinal anatomy in four species of elasmobranch. J. Morphol., 273: 423–440. doi: 10.1002/jmor.11033
- Issue online: 29 FEB 2012
- Version of Record online: 24 NOV 2011
- Manuscript Accepted: 26 SEP 2011
- Manuscript Revised: 23 SEP 2011
- Manuscript Received: 15 AUG 2011
- Australian Research Council QEII Fellowship/Discovery Project. Grant Number: DP0558681
Using both light and transmission electron microscopy, we examined the retinal anatomy of four elasmobranch species with differing ecologies: the bull shark Carcharhinus leucas, Port Jackson shark Heterodontus portusjacksoni, epaulette shark Hemiscyllium ocellatum and pink whipray Himantura fai. Their retinas are typical of other vertebrates, having three nuclear and two synaptic layers, but are characterised by very large horizontal cells, low densities of ganglion cells (many of which are displaced to the inner nuclear and inner plexiform layers) and the presence of numerous myelinated axons within the nerve fibre layer. Carcharhinus leucas, H. fai and H. ocellatum have duplex retinas containing both rods and single cones. The peak ratio of rods to cones is much lower in C. leucas (4:1) and H. fai (3:1) compared to H. ocellatum (19:1), reflecting differences in diel activity patterns. No cones were observed in the retina of H. portusjacksoni, which is strongly nocturnal. The cones of H. fai lack a distinct myoid and their nuclei are located in a discrete layer sclerad to the external limiting membrane (ELM), whereas those of C. leucas and H. ocellatum have an obvious myoid, and their nuclei are located vitread to the ELM. No double/twin cones were observed in any species. Incorporating data from other studies, there is a clear correlation between rod outer segment volume and visual ecology in elasmobranchs, with smaller volumes found in partly diurnal pelagic species and larger volumes in benthic nocturnal species. This trend may reflect fundamental differences in visual temporal resolution between active and more sedentary species. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.