Ultraviolet Vision Essay

Submitted By kemilyv
Words: 1517
Pages: 7

Ultraviolet vision is less commonly known as tetrachromacy which is a condition in which you have four different colour channels and are able to process colour differently than those without the four different types of cone cells. There are different types of wavelengths that are involved in vision. Blue waves are short wavelengths and they focus at shorter distances whereas red waves are long wavelengths and focus at much long wavelengths (Gustafsson, Collin, Kroger, 2008). According to Gerald Jacobs there is evidence that there are retinal photo pigments that allow for ultraviolet vision to be common and found in many different classes such as amphibians, reptiles as well as mammals. Over the course of this paper, the different types of tetrapods and the use of their ultraviolet vision will be discussed as well as their different types of vision.
In a vertebrate, there is two parts to the retina that respond to light, they are: rods, which mediate achromatic vision at low lighting and cones, which mediate chromatic vision at high levels of light. (Hoog et al., 2011) Rods, being sensitive to wavelengths, this enables them to be sensitive to low light levels but they do not produce a very high visual acuity. (Pough, 2009) There is a subgroup of cells within the cone cells of the retina that contain pigments that are highly sensitive to different wavelengths of light. Cone cells require a high level of illumination compared to that of the rods cells because only a few cone cells transmit their responses to a bipolar cell. Overall, cones cells produce much clearer images than rod cells. There are many ideas and assumptions about ultraviolet (UV) vision, according to Jacobs, he said that many have made suggestions to the way that UV sensitivity might be used for making important discriminations used during food gathering as well as detecting other predators. It is also said that it may aid in polarized light.
Birds have a high need for UV vision for foraging foods like insects, berries and seeds. The wavelengths are important because of the fact that they basically depend on the reflectance of the prey. While the background is also important especially with insects because it is usually a tree or the ground which does not reflect UV light like natural backgrounds do. Birds are also extremely sensitive to UV wavelengths and are actually able to see wavelengths that humans are unable to detect. As for fruits and berries, the UV waves reflect off of those that have wax on them and therefore attract the birds. In a study, it was shown that foraging for food and being attracted to the waxy fruit was most likely a learned trait because the younger birds were not necessarily attracted to the wax fruit. It is even thought to be possible that they likely possess four dimensional colour vision. There have been studies done to show evidence that birds do indeed use ultraviolet waves to forage. Many studies are done on pigeons (Columba livia) as they are a popular lab animal. They showed a high sensitivity to the UV wavelengths and it was shown that the pigeons were able to forage successfully even though the seeds were on a diffusing plate that was lit up by UV light.
The next tetrapods discussed are fishes that are also known to have ultraviolet vision. There have been people able to train fish to make different choices behaviorally, while choosing between different colours but they failed to be able to control the brightness of the colours. (Bone, Marshall & Blaxter, 1995) How fish make use of the UV information is uncertain, but it has evolved. The vivid colours of fish in shallow waters indicate coloured vision and they also enhances contrast so that their prey and enemies are more noticeable. (Bone, Marshall & Blaxter, 1995) Measurements of the penetration of ultraviolet light into the shallow waters shows us that they make effective use of the information retrieved from the wavelengths. (Loew and McFarland, 1990) As quoted by