Meeting Abstract

P2.65  Friday, Jan. 4  Comparative optic nerve and optic foramen size in nocturnal and diurnal raptors HALL, MI*; ROSENSTEIN, SL; Midwestern University, Glendale; Midwestern University, Glendale margaretihall@yahoo.com

Nocturnal and diurnal vertebrates often exhibit differences in retinal wiring, specifically with regard to �retinal pooling,� or the number of photoreceptor cells providing information to a single ganglion cell in the retina. Diurnal birds are expected to have low retinal pooling, which acts to increase acuity, since each photoreceptor cell is responsible for a proportional angle of visual space. Nocturnal birds, in contrast, may have high retinal pooling; if multiple photoreceptors provide information to a single ganglion cell, that ganglion cell will be excited if any one of those photoreceptor cells capture a light particle, which greatly increases light sensitivity. The optic nerve is comprised of the ganglion cell axons delivering information to the brain. This study tests the hypothesis that nocturnal raptors will have a relatively smaller optic nerve and therefore a relatively smaller bony optic foramen than diurnal raptors, based on differences in retinal pooling between the two groups. This study included species of Strigidae, Tytonidae, Accipitidrae, and Falconidae, avian taxa of varying activity pattern but similar ecologies. Dissections on wet specimens (3 Tyto, 2 Bubo, 1 Buteo, 2 Accipiter, and 2 Falco) verified that in all dissected birds there is a very close relationship between the optic foramen and optic nerve. Subsequently, optic foramen size was measured on 90 dry specimens of 40 nocturnal and diurnal species of the above-mentioned groups. ANOVA and regression analyses indicate a significant difference between the optic foramen sizes, with diurnal birds consistently exhibiting a larger optic foramen than nocturnal birds.