Lisney Thomas J, Iwaniuk Andrew N, Bandet Mischa V, Wylie Douglas R
Department of Psychology, University of Alberta, Edmonton, Canada.
Brain Behav Evol. 2012;79(4):218-36. doi: 10.1159/000337760. Epub 2012 Jun 18.
The eyes of vertebrates show adaptations to the visual environments in which they evolve. For example, eye shape is associated with activity pattern, while retinal topography is related to the symmetry or 'openness' of the habitat of a species. Although these relationships are well documented in many vertebrates including birds, the extent to which they hold true for species within the same avian order is not well understood. Owls (Strigiformes) represent an ideal group for the study of interspecific variation in the avian visual system because they are one of very few avian orders to contain species that vary in both activity pattern and habitat preference. Here, we examined interspecific variation in eye shape and retinal topography in nine species of owl. Eye shape (the ratio of corneal diameter to eye axial length) differed among species, with nocturnal species having relatively larger corneal diameters than diurnal species. All the owl species have an area of high retinal ganglion cell (RGC) density in the temporal retina and a visual streak of increased cell density extending across the central retina from temporal to nasal. However, the organization and degree of elongation of the visual streak varied considerably among species and this variation was quantified using H:V ratios. Species that live in open habitats and/or that are more diurnally active have well-defined, elongated visual streaks and high H:V ratios (3.88-2.33). In contrast, most nocturnal and/or forest-dwelling owls have a poorly defined visual streak, a more radially symmetrical arrangement of RGCs and lower H:V ratios (1.77-1.27). The results of a hierarchical cluster analysis indicate that the apparent interspecific variation is associated with activity pattern and habitat as opposed to the phylogenetic relationships among species. In seven species, the presence of a fovea was confirmed and it is suggested that all strigid owls may possess a fovea, whereas the tytonid barn owl (Tyto alba) does not. A size-frequency analysis of cell soma area indicates that a number of different RGC classes are represented in owls, including a population of large RGCs (cell soma area >150 µm(2)) that resemble the giant RGCs reported in other vertebrates. In conclusion, eye shape and retinal topography in owls vary among species and this variation is associated with different activity patterns and habitat preferences, thereby supporting similar observations in other vertebrates.
脊椎动物的眼睛呈现出对其进化所处视觉环境的适应性。例如，眼睛形状与活动模式相关，而视网膜地形图则与物种栖息地的对称性或“开阔程度”有关。尽管这些关系在包括鸟类在内的许多脊椎动物中都有详尽记录，但对于同一目鸟类中的物种而言，这些关系在多大程度上成立却并不十分清楚。猫头鹰（鸮形目）是研究鸟类视觉系统种间变异的理想类群，因为它们是极少数在活动模式和栖息地偏好上都存在差异的鸟类目之一。在此，我们研究了9种猫头鹰的眼睛形状和视网膜地形图的种间变异。种间眼睛形状（角膜直径与眼轴长度之比）存在差异，夜行性物种的角膜直径相对大于日行性物种。所有猫头鹰物种在颞侧视网膜都有一个视网膜神经节细胞（RGC）高密度区域，并且有一条细胞密度增加的视觉带，从颞侧延伸至鼻侧穿过中央视网膜。然而，视觉带的组织和伸长程度在种间差异很大，这种差异通过H:V比值进行量化。生活在开阔栖息地和/或日行性更强的物种具有明确、伸长的视觉带和高H:V比值（3.88 - 2.33）。相反，大多数夜行性和/或栖息在森林中的猫头鹰视觉带不明确，RGC的排列更呈放射状对称，H:V比值较低（1.77 - 1.27）。层次聚类分析结果表明，明显的种间变异与活动模式和栖息地有关，而非物种间的系统发育关系。在7个物种中确认了中央凹的存在，并且有人提出所有鸱鸮科猫头鹰可能都拥有中央凹，而草鸮科仓鸮（Tyto alba）则没有。细胞体面积的大小频率分析表明，猫头鹰中存在许多不同的RGC类别，包括一群大型RGC（细胞体面积>150 µm²），类似于其他脊椎动物中报道的巨型RGC。总之，猫头鹰中眼睛形状和视网膜地形图在种间存在差异，这种差异与不同的活动模式和栖息地偏好相关，从而支持了在其他脊椎动物中观察到的类似现象。
