TY - JOUR
T1 - Ontogenetic changes in retinal ganglion cell distribution and spatial resolving power in the brown-banded bamboo shark chiloscyllium punctatum (elasmobranchii)
AU - Harahush, Blake K.
AU - Hart, Nathan S.
AU - Collin, Shaun P.
PY - 2014
Y1 - 2014
N2 - The development of the visual system in anamniotic vertebrates is a continual process, allowing for ontogenetic changes in retinal topography and spatial resolving power. We examined the number and distribution of retinal ganglion cells in wholemounted retinae throughout the protracted embryonic development (∼5 months) of a chondrichthyan, i.e. the brown-banded bamboo shark Chiloscyllium punctatum, from the beginning of retinal cell differentiation (approximately halfway through embryogenesis) to adulthood. We also identified and quantified the number of apoptosed cells within the ganglion cell layer to evaluate the contribution of apoptosis to changes in retinal topography. C. punctatum undergoes rapid changes in ganglion cell distribution during embryogenesis, where high levels of apoptosis, especially around the retinal periphery, result in relative increases in ganglion cell density in the central retina which progressively extend nasally and temporally to form a meridional band at hatching. After hatching, C. punctatum forms and maintains a horizontal streak, showing only minor changes in topography during growth, with basal levels of apoptosis. The total number of retinal ganglion cells reaches 547,881 in adult sharks, but the mean (3,228 cells·mm-2) and peak (4,983 cells·mm-2) retinal ganglion cell densities are highest around the time of hatching. Calculated estimates of spatial resolving power, based on ganglion cell spacing (assuming a hexagonal mosaic) and assessment of the focal length from cryosections of the eye, increase from 1.47 cycles·degree-1 during embryogenesis to 4.29 cycles·degree-1 in adults. The increase in spatial resolving power across the retinal meridian would allow this species to hunt and track faster, more mobile prey as it reaches maturity.
AB - The development of the visual system in anamniotic vertebrates is a continual process, allowing for ontogenetic changes in retinal topography and spatial resolving power. We examined the number and distribution of retinal ganglion cells in wholemounted retinae throughout the protracted embryonic development (∼5 months) of a chondrichthyan, i.e. the brown-banded bamboo shark Chiloscyllium punctatum, from the beginning of retinal cell differentiation (approximately halfway through embryogenesis) to adulthood. We also identified and quantified the number of apoptosed cells within the ganglion cell layer to evaluate the contribution of apoptosis to changes in retinal topography. C. punctatum undergoes rapid changes in ganglion cell distribution during embryogenesis, where high levels of apoptosis, especially around the retinal periphery, result in relative increases in ganglion cell density in the central retina which progressively extend nasally and temporally to form a meridional band at hatching. After hatching, C. punctatum forms and maintains a horizontal streak, showing only minor changes in topography during growth, with basal levels of apoptosis. The total number of retinal ganglion cells reaches 547,881 in adult sharks, but the mean (3,228 cells·mm-2) and peak (4,983 cells·mm-2) retinal ganglion cell densities are highest around the time of hatching. Calculated estimates of spatial resolving power, based on ganglion cell spacing (assuming a hexagonal mosaic) and assessment of the focal length from cryosections of the eye, increase from 1.47 cycles·degree-1 during embryogenesis to 4.29 cycles·degree-1 in adults. The increase in spatial resolving power across the retinal meridian would allow this species to hunt and track faster, more mobile prey as it reaches maturity.
UR - http://www.scopus.com/inward/record.url?scp=84924920598&partnerID=8YFLogxK
U2 - 10.1159/000361036
DO - 10.1159/000361036
M3 - Article
C2 - 24993335
AN - SCOPUS:84924920598
SN - 0006-8977
VL - 83
SP - 286
EP - 300
JO - Brain, Behavior and Evolution
JF - Brain, Behavior and Evolution
IS - 4
ER -