Visual Sensory Processing
Fig. 14. Aonyx cinereus. (Photograph by Chris. “Asian Small-clawed Otter - Aonyx cinereus,” Animal Keeper [2011]. Retrieved November 12, 2021, from https://animalkeeper91.blogspot.com/2011/03/asian-small-clawed-otter-aonyx-cinereus.html)
According to Hamman (2004), Aonyx cinereus pups are born with their eyes closed, see figure 14, and they do not open until around 40 days. Like many other mammals, they are semi-aquatic. Over time, their bodies have evolved in specialized ways that allow them to function not only on land but also in water. Their sensory processes, such as vision, have adapted to perform effectively in two drastically different environments.
Light transmits differently in water than it does in air, presenting an optical dilemma for the eye and requiring adaptions in the cornea and lens. These adaptions control the amount of light entering the eye, and the direction light is refracted, (Strobel et al., 2020, 768). The pupil also plays a major role for semiaquatic mammals, restricting and dilating during deep dives and when re-surfacing.
A. cinereus rely heavily on eyesight for hunting, and as such, they require
visual acuity for both types of environments. According to Seaworld Parks & Entertainment (n.d.), their lens and cornea correct the refraction of light caused by the transition from aerial to aquatic vision. It is because of this correction that their vision in light is equally good in both environments, although in dim light it is better in air.
Despite the disadvantage of lesser sight in water during dim light, they do still maintain an ability to see well at nighttime, due to the presence of the tapetum lucidum, shown in figure 15. This is an additional tissue layer that
sits behind the retina, acting as a reflective layer, (Mccartan, 2020). If you’ve ever taken a flash-assisted photo of your cat or dog at night, you may recognize the eerie eye glow that it causes, as demonstrated by figure 16.
Although the sensory processes of A. cinereus have not been extensively studied, the presence of potential color vision has recently come under investigation. Upon completing the first study on this, with results providing only preliminary evidence, Svoke et al., (2014, 182) were confident that, “Asian small-clawed otters, as well as most likely all otter species, have the ability to see color.” Despite this, further investigation is required to better understand not only color vision but the vision of A. cinereus overall.
