A comparative study of the distribution and density of retinal ganglion cells and visual acuity in Bothrops snakes with differences in the habitat use

Abstract

Purpose : The density and distribution of neurons in retinas of vertebrates are associated with speci c behaviors and species ecology. The visual system of snakes has adaptations to the species' habitats, circadian rhythm, and foraging strategies. A previous study revealed a ventral area centralis in a terrestrial snake and a visual streak in a close related arboreal species. In this study, we compared the distribution of ganglion cell layer (GCL) cells in retinas of Viperidae snakes from the genus Bothrops, with differences in the habitat use, namely the arboreal B. insularis, and the semi-arboreal species B. jararaca and B. sazimai. In the present study, we observed a poorly defined horizontal streak in retinas of the arboreal B. insularis, with higher density in the central retina, while in the semi-arboreal B. jararaca and B. sazimai there were no defined retinal specializations, and the peak cell densities were located in the temporal region. These findings reinforce the hypothesis that retinal specializations are associated with habitat use in snakes. A visual streak may assist in locomotion and hunting among branches, as indicated by the distribution of cells in B. insularis. On the other hand, peak GCL cell density in the temporal retina may facilitate striking behavior in the species that forage on the ground.

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ARVO Annual Meeting Abstract| June 2020
A comparative study of the distribution and
density of retinal ganglion cells and visual
acuity in Bothrops snakes with differences
in the habitat use
Christinia Patel; Juliana Tashiro; Einat Hauzman; Karina Banci; Malinda EC Fitzgerald; Dora Fix Ventura
 Author Aliations & Notes
Investigative Ophthalmology & Visual Science June 2020, Vol.61, 4517. doi:
Abstract
Purpose : The density and distribution of neurons in retinas of vertebrates are
associated with specic behaviors and species ecology. The visual system of snakes has
adaptations to the species’ habitats, circadian rhythm, and foraging strategies. A
previous study revealed a ventral area centralis in a terrestrial snake and a visual streak
in a close related arboreal species. In this study, we compared the distribution of
ganglion cell layer (GCL) cells in retinas of Viperidae snakes from the genus Bothrops,
with dierences in the habitat use, namely the arboreal B. insularis, and the semi-
arboreal species B. jararaca and B. sazimai.
Methods : Three individuals of each species were euthanized with Thionembutal (100
mg/kg). The eyes were enucleated and retinas were dissected and xed in 4%
paraformaldehyde. Retinas were wholemounted and Nissl stained. The density of GCL
cells was estimated using a stereological approach with the Stereo Investigator
software (MicroBrightField), and isodensity maps were obtained using OriginPro 8.5.1.
Visual acuity values were estimated based on the peak density of GCL cells and the eyes
focal length.
Results : We observed a poorly dened horizontal streak in retinas of the arboreal B.
insularis, with higher density in the central retina, while in the semi-arboreal B. jararaca
and B. sazimai there were no dened retinal specializations, and the peak cell densities
were located in the temporal region. The mean cell density was 4,405 ± 735 cells/mm2
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in B. insularis, 4,606 ± 335 cells/mm in B. sazimai, and 4,881 ± 746 cells/mm in B.
jararaca. The estimated spatial resolutions were similar among the species and varied
from 2.0 to 2.2 cycles per degree.
Conclusions : These ndings reinforce the hypothesis that retinal specializations are
associated with habitat use in snakes. A visual streak may assist in locomotion and
hunting among branches, as indicated by the distribution of cells in B. insularis. On the
other hand, peak GCL cell density in the temporal retina may facilitate striking behavior
in the species that forage on the ground.
This is a 2020 ARVO Annual Meeting abstract.
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Fig. 1. Distribution of GCL cells in Bothrops snakes. The isodensity values in cells/mm
are represented by the grayscale. The white circles indicate the optic nerves. D, dorsal;
T, temporal. Scale bars: 4 mm.
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