Evolution of Tapetum Lucidum

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Human Eye Vs. Animal EyeBy:Andrea Torres

The tapetum lucidum is an evolutionary advantage for animals. It enables animals to see in dimmer light than the animal would otherwise be able to see in. The tapetum lucidum is useful to animals, but it also has a use to humans. Human beings use the tapetum lucidum to scan for reflected eye-shine, in order to detect and identify the species of animals in the dark and to send trained search dogs and search horses out at night. Historically, its function was regarded as simply to increase the light intensity of an image on the retina. Using eye shine to identify animals in the dark implies not only color but, also several other features. The color reciprocates to the type of tapetum lucidum with some distinction between species. Other features also include the distance between pupils’ related to its size, the height above the ground; the manner of blinking, (if there is any) and the movement of the eye shine (such as weaving, hopping, leaping, climbing or flying.) Tapetum cellulosum was discovered in the eyes of sharks, sturgeons, and coelacanths, suggesting that it may have been the first type of tapetum to evolve in vertebrates. These species have similar enough tapeta that they may have had a common ancestor with a tapetum developing at approximately the Devonian period or, at the earliest, the very late Silurian. INTRODUCTION

The tapetum lucidum, in Latin it means “shining carpet”, a layer of the tissue in the eye of vertebrate and invertebrate animals. The tapetum is proximal to the photoreceptors and may be located in either the retina in vertebrate animals and proximal to the reticular cells in invertebrates animals. The "shining carpet" reflects visible light back through the retina increasing the light available for photo receptors. The tapetum reflects the photons that are not initially absorbed after they are passed through the photoreceptors. These reflector mechanisms are able to provide the photoreceptors a second chance at absorbing the reflected light, therefore it can enhance an organism's visual sensitivity. This improves low light conditions but can also cause the perceived image to be blurry from the interference of the reflected light. The tapetum lucidum contributes to the superior night vision of some animals. This device is often a layer, and is especially useful in lower light conditions. Animals use a wide range of materials and different techniques to provide tapetal reflectance, including guanine, riboflavin, triglycerides, pteridine, cholesterol, zinc, astaxanthin and collagen. Historically, tapeta has evolved several times with different mechanisms and they represent convergent evolution of function. Tapetum lucidum is found in many animals that are nocturnal, especially carnivores, that hunt and prey at night, while others are deep sea animals. Human-beings do not have a tapetum lucidum. EVOLUTION OF THE TAPETUM

The evolution of the tapetum will most-likely never be determined. Vertebrates are believed to have evolved from the pikaia, a primitive invertebrate and an ancestor to the modern-day amphioxus. The pikaia existed in the Precambrian Era, about 430 million years ago. Tapeta does not occur in amphioxus or agnatha; therefore, its only assumptions that tapeta did not exist in the ostracoderms. In the Devonian Period, 345-395 years ago; all three orders may have developed tapeta independently from each other (sharks,sturgeons and lobe-finned fish). These three orders of fish all possess a tapetum cellulosum, indicating that this tapetum may have been the first type of tapetum to evolve in vertebrates. These species have similarities that they may have had a common ancestor with a tapetum developing during the Deornian period or at the earliest, the very late Silurian. The development of the tapetum independently in fish might have occurred to allow them to explore deeper depths of the ocean, where light was not prevalent....
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