81-5 Sat Jan 2 oculomotor nuclei size reflects behavior in nocturnal and diurnal raptors Cunha, F*; Gutiérrez-Ibáñez, C; Wylie, DR; Iwaniuk, AN; Univ. of Lethbridge, Canada; Univ. of Alberta, Canada; Univ. of Alberta, Canada; Univ. of Lethbridge, Canada felipebrcunha@gmail.com
Eye movements are a critical component of visually guided behaviors in animals. Although the control of these movements by cranial nerve nuclei is conserved across clades, species variation in visually guided behavior and eye morphology could lead to variation in the size of oculomotor nuclei. Here, we test for differences in the size of the oculomotor nuclei among bird clades that vary in behavior and eye morphology. The volumes and neuron numbers of the oculomotor (nIII), trochlear (nIV), abducens (nVI) and Edinger-Westphal nuclei were quantified across 60+ bird species. Our comparative analyses show that owls and New World vultures have relatively smaller nIII, nIV and nVI nuclei and hawks have relatively large nIII and nVI nuclei compared with other clades. The relatively small oculomotor nuclei of owls are likely due to their unique tubular eye shape, which markedly constrains eye movements to a few degrees at most. Hawks are somewhat unique among birds in that the retina has two foveae located centrally and temporally. Hawks need to visually target in pursuit of moving prey, and likely require binocular frontal vision upon the grasping of the prey. Such behavior is likely dependent on extensive eye movements, resulting in the evolution of an enlarged nIII. Although vultures are closely related to hawks and have two areas of specialization in the retina, the temporal area is not a fovea and has lower spatial resolving power. Vultures only scavenge carrion and therefore are unlikely to rely as much on extensive eye movements. We conclude that the relative size of the oculomotor nuclei reflects visually guided behavior in birds, but more data is needed on eye movements in birds to better understand the evolution of their visual system.