Supplementary Material for: Retinal ganglion cell topography and spatial resolution in three Indian pteropodid bats

Pteropodidae is the only phytophagous bat family that predominantly depends on visual and olfactory cues for orientation and foraging. During daytime, pteropodids of different species roost in sites with varying light exposure. Pteropodids have larger eyes relative to body size than insectivorous bats. Retinal topography has been studied in less than 10% of the approximately 200 pteropodid species, a behavioural estimation of spatial resolution is available only for Pteropus giganteus, and little is known about the relationship between their roost site preference and visual ecology. We present retinal ganglion cell topographic maps and anatomical estimates of spatial resolution in three southern Indian pteropodid species with different roosting preferences. Ganglion cell densities are between 1000 and 2000 cells/mm2 in the central retina and lower in the dorsal and ventral periphery. All three species have a temporal area in the retina with peak ganglion cell densities of 4600 to 6600 cells/mm2. As a result, the foliage-roosting Cynopterus sphinx and the cave-roosting Rousettus leschenaultii have similar anatomical resolution (2.7 and 2.8 cycles/degree, respectively). The anatomical estimate for the larger tree-roosting P. giganteus (4.0 cycles/degree) is higher than the spatial resolution determined earlier in behavioural tests. Like other pteropodids and unlike other vertebrates, all three species have choroidal papillae. Based on 15 pteropodid species studied to date, we find no relationship between roost type and eye size or visual acuity. For a general understanding of the sensory ecology of pteropodids that perform key ecosystem services in the tropics, it will be essential to study additional species.

狐蝠科（Pteropodidae）是唯一一类主要依赖视觉与嗅觉线索完成定向与觅食活动的植食性蝙蝠类群。日间，不同物种的狐蝠会栖息于光照条件各异的位点。相较于食虫蝙蝠，狐蝠的眼睛相对体型比例更大。目前，在约200种狐蝠中，仅不到10%的物种被开展过视网膜拓扑结构（retinal topography）研究，且仅大狐蝠（Pteropus giganteus）有行为学层面的空间分辨率（spatial resolution）估算数据，关于其栖息位点偏好与视觉生态之间的关联则所知甚少。本研究报道了3种栖息偏好各异的印度南部狐蝠物种的视网膜神经节细胞（retinal ganglion cell）拓扑图谱，以及空间分辨率的解剖学估算结果。3个物种的视网膜中央区神经节细胞密度介于1000~2000个/mm²，背侧与腹侧周边区的密度相对更低。所有3个物种的视网膜颞侧均存在神经节细胞密度峰值区，峰值密度为4600~6600个/mm²。据此，叶栖的犬蝠（Cynopterus sphinx）与穴栖的莱氏狐蝠（Rousettus leschenaultii）拥有相近的解剖学空间分辨率（分别为2.7与2.8个周期/度）。体型更大的树栖大狐蝠（P. giganteus）的解剖学估算分辨率（4.0个周期/度），高于此前行为学测试所测得的空间分辨率。与其他狐蝠一致、且区别于其他脊椎动物的是，这3个物种均拥有脉络膜乳头（choroidal papillae）。基于迄今已开展研究的15种狐蝠物种，我们未发现栖息类型与眼睛大小或视敏度之间存在关联。对于理解在热带生态系统中发挥关键生态系统服务功能的狐蝠的感官生态学而言，开展更多物种的相关研究至关重要。