Dirunal vs. Nocturnal Felines:
Part I - Anatomical Differences
Many studies have been done as to the differences in how vision works between nocturnal and diurnal animals. There are differences at both the anatomical and physiological levels:
One study was performed to see the differences in retinal S and M cone topographies of both diurnal and nocturnal felines. There are three types of cones in the eye: L, S, and M. L cones respond to light of long wavelengths, M cones to medium wavelengths, and S to short wavelengths. The difference in the signals received from the three cone types allows the brain to perceive color and light (Ahnelt et al., 2006). Thus a study was performed to see if cones in diurnal felines differed from cones in nocturnal felines. The results showed that in the domestic cat (a nocturnal feline) there was a very high density of S cone receptors, whereas the cheetah (a diurnal feline) had a much higher density of M cone receptors. In conclusion, it is generally reasonable to assume that a higher density of S cones and S cone receptors should enable better detection of spectrally distinct items (Ahnelt et al., 2006). Thus it makes sense for nocturnal felines to have a higher density of S cones. It is more difficult to see in the dark, and thus a nocturnal feline needs to detect light at lower frequencies in order to see better. A higher density of S cones allows the feline to detect prey and predators easier during the night. However, an animal that hunts during the day does not need this advantage and would prefer to see better during the day, which is why the diurnal feline has a higher M cone density. The results of this experiment make practical sense for what diurnal and nocturnal felines need to survive.
Close-up of a cheetah's eyes (a diurnal feline). Image courtesy of www.vivisto.co.uk
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