Supplementary Material for: Retinal Ganglion Cell Topography and Spatial Resolving Power in Echolocating and Non-Echolocating Bats

Bats are nocturnal mammals known for their ability to echolocate, yet all bats can see, and most bats of the family Pteropodidae (fruit bats) do not echolocate – instead they rely mainly on vision and olfaction to forage. We investigated whether echolocating bats, given their limited reliance on vision, have poorer spatial resolving power (SRP) than pteropodids and whether tongue click echolocating fruit bats differ from non-echolocating fruit bats in terms of visual performance. We compared the number and distribution of retinal ganglion cells (RGCs) as well as the maximum anatomical SRP derived from these distributions in 4 species of bats: <i>Myotis daubentonii</i>, a laryngeal echolocating bat from the family Vespertilionidae, <i>Rousettus aegyptiacus</i>, a tongue clicking echolocating bat from the family Pteropodidae, and <i>Pteropus alecto</i> and <i>P. poliocephalus</i>, 2 non-echolocating bats (also from the Pteropodidae). We find that all 3 pteropodids have a similar number (≈200,000 cells) and distribution of RGCs and a similar maximum SRP (≈4 cycles/degree). <i>M. daubentonii</i> has fewer (∼6,000 cells) and sparser RGCs than the pteropodids and thus a significantly lower SRP (0.6 cycles/degree). <i>M. daubentonii</i> also differs in terms of the distribution of RGCs by having a unique dorsal area of specialization in the retina. Our findings are consistent with the existing literature and suggest that <i>M. daubentonii</i> likely only uses vision for orientation, while for pteropodids vision is also important for foraging.

蝙蝠是一类以回声定位（echolocate）能力闻名的夜行性哺乳动物，但所有蝙蝠均具备视觉能力，且狐蝠科（Pteropodidae）的多数蝙蝠（果蝠）并不具备回声定位能力——它们主要依靠视觉与嗅觉来觅食。本研究旨在探究依赖回声定位的蝙蝠是否因对视觉的依赖程度较低，而相较于狐蝠科蝙蝠具有更弱的空间分辨力（spatial resolving power, SRP），同时探究以舌部咔哒声进行回声定位的果蝠与非回声定位果蝠在视觉表现上是否存在差异。我们比较了4种蝙蝠的视网膜神经节细胞（retinal ganglion cells, RGCs）数量与分布特征，以及基于这些分布推导得到的最大解剖学空间分辨力：分别是隶属于蝙蝠科（Vespertilionidae）的喉部回声定位蝙蝠——*Myotis daubentonii*（水鼠耳蝠）、隶属于狐蝠科的舌部回声定位蝙蝠——*Rousettus aegyptiacus*（埃及果蝠），以及2种非回声定位狐蝠：*Pteropus alecto*（澳洲狐蝠）和*P. poliocephalus*（灰头狐蝠）。研究结果显示，3种狐蝠科蝙蝠的视网膜神经节细胞数量（约20万个）与分布特征相近，最大空间分辨力也基本一致（约4个周期/度）。相较于狐蝠科蝙蝠，*Myotis daubentonii*（水鼠耳蝠）的视网膜神经节细胞数量更少（约6000个）且分布更稀疏，因此其空间分辨力显著更低（0.6个周期/度）。此外，水鼠耳蝠的视网膜神经节细胞分布存在独特的背部特化区域，这一点也与其他物种不同。本研究结果与现有文献相符，表明水鼠耳蝠可能仅将视觉用于定向，而狐蝠科蝙蝠的视觉对觅食同样至关重要。