The Topographic Organization of Retinal Ganglion Cell Density and Spatial Resolving Power in an Unusual Arboreal and Slow-Moving Strepsirhine Primate, the Potto <b><i>(Perodicticus potto)</i></b>

Abstract

The potto (Perodicticus potto) is an arboreal strepsirhine found in the rainforests of central Africa. In contrast to most primates, the potto shows slow-moving locomotion over the upper surface of branches, where it forages for exudates and crawling invertebrates with its head held very close to the substrate. Here, we asked whether the retina of the potto displays topographic specializations in neuronal density that correlate with its unusual lifestyle. Using stereology and retinal wholemounts, we measured the total number and topographic distribution of retinal ganglion cells (total and presumed parasol), as well as estimating the upper limits of the spatial resolution of the potto eye. We estimated ∼210,000 retinal ganglion cells, of which ∼7% (∼14,000) comprise presumed parasol ganglion cells. The topographic distribution of both total and parasol ganglion cells reveals a concentric centroperipheral organization with a nasoventral asymmetry. Combined with the upwardly shifted orbits of the potto, this nasoventral increase in parasol ganglion cell density enhances contrast sensitivity and motion detection skywards, which potentially assists with the detection of predators in the high canopy. The central area of the potto occurs ∼2.5 mm temporal to the optic disc and contains a maximum ganglion cell density of ∼4,300 cells/mm². We found no anatomical evidence of a fovea within this region. Using maximum ganglion cell density and eye size (∼14 mm), we estimated upper limits of spatial resolving power between 4.1 and 4.4 cycles/degree. Despite their reported reliance on olfaction to detect exudates, this level of spatial resolution potentially assists pottos with foraging for small invertebrates and in the detection of predators.

Retinal ganglion cell topography and spatial resolving power in the river hippopotamus (Hippopotamus amphibius)

“…To distinguish retinal ganglion cells from amacrine and glial cells in the river hippopotamus Nissl‐stained wholemount, we used well‐established cytological criteria proposed by Hughes (). These criteria have been validated in a range of mammals including artiodactyls (Coimbra, Kaswera‐Kyamakya, Gilissen, Manger, & Collin, ; Coimbra, Kaswera‐Kyamakya, Gilissen, Manger, & Collin, ; Coimbra, Kaswera‐Kyamakya, Gilissen, Collin, & Manger, 2017; Coimbra & Manger, ; Coimbra et al, ; Mass & Supin, ; Peichl, ; Silveira, Picanço‐Diniz, & Oswaldo‐Cruz, ; Silveira, Picanço‐Diniz, Sampaio, & Oswaldo‐Cruz, ; Wong, Wye‐Dvorak, & Henry, ). Cell profiles showing polygonal soma with dense accumulations of Nissl substance in the cytoplasm, an eccentric nucleus and a prominent nucleolus were classified as retinal ganglion cells (Figure C,D).…”

Diversity of photoreceptor arrangements in nocturnal, cathemeral and diurnal Malagasy lemurs

“…Even the diurnal species P. verreauxi, L. catta, and I. indri possess a tapetum, indicating that their eyes are adapted to cathemerality rather than diurnality. It appears that a tapetum is an ancestral feature of Strepsirrhini, as it also is present in the lorisiform branch (Coimbra, Kaswera-Kyamakya, Gilissen, Manger, & Collin, 2016;Dartnall et al, 1965;Pariente, 1976;Pirie, 1959), whereas a tapetum is absent in the Haplorrhini, even in the nocturnal Tarsius and Aotus (review: Heesy & Ross, 2001).…”

Retinal ganglion cell topography and spatial resolving power in African megachiropterans: Influence of roosting microhabitat and foraging

“…To distinguish ganglion cells from amacrine and glial cells, we used well-established cytological criteria proposed by Hughes (1981) and validated in a range of mammal species (Wong et al, 1986;Silveira et al, 1989aSilveira et al, ,b, 1993Peichl, 1992;Mass and Supin, 1992, 2010Hanke et al, 2009;Coimbra et al, 2013Coimbra et al, , 2015bCoimbra et al, , 2016. Cell profiles showing a polygonal soma with dense accumulations of Nissl substance in the cytoplasm, an eccentric nucleus, and a prominent nucleolus were classified as retinal ganglion cells (Fig.…”