Shubin mentions the advantages of vision (capturing light to process images) in Chapter 9 (148). The ability to see provides organisms such as humans with a great evolutionary advantage, as oppose to an organism without eyes, forced to use other senses by means of getting around such as sharpening their sense of smell. With eyesight, animals gain the ability to be more functional and optimize their ability as scavengers. Discuss how eyes vary among others, such as differences in invertebrates and vertebrates. How has eye structure developed differently overtime in such invertebrates, flies and worms? How is eye structure shared among different species?
Kyle Kim, piece847@gmail.com
There are many different types of organs and tissues that animals use in order to capture light. Humans and other vertebrates have camera-like eyes while invertebrate animals have “simple photoreceptor organs” (149) that they use as eyes. Not all invertebrates share the same photoreceptor organs, however. For example, sea urchins lack a definite eye. They detect light by their tube feet which are thought to act as photosensory organs. Flies have “eyes with compound lenses” (150). These flies along with other arthropods have eyes made up of repeating units called ommatidia. Each of these units functions as a separate visual receptor. The compound lenses flies have are completely different to how worms “see”. Unlike in flies with their many lenses, worms don’t have any eyes. Instead they have light receptors (photoreceptors) on their skin. These photoreceptors are located on nerve fibers along the skin of the worm.
ReplyDeleteIn squid and octopi, the eye is almost the same as the eye in vertebrates. The one difference is that a vertebrate eye is “reversed” while the cephalopods’ eyes are not. This means that in vertebrates, the inner layer of the double walled optic cup becomes the retina. So, the light-sensitive portion of the eye (rods and cones) ends up on the outside. Therefore, light has to go through all of the layers before it reaches the rods and cones. In the squid and octopi eyes, it is the opposite where the light sensitive portion is on the inside surface. One thing that all eyes have in common, vertebrate or invertebrate, is that they each use the same kind of light-capturing molecule to help them see: “Insects, humans, clams, and scallops all use opsins” (152). Opsins are molecules that convey information from the outside of a cell to the inside. The opsins carry a chemical across the membrane of a cell with a conductor “that takes a series of bends and loops as it travels from the outside to the inside of the cell” (152).
Sources:
Your Inner Fish
http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab11/Eye/NOTES/EYENOTE.HTM
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CompoundEye.html
http://www.ehow.com/facts_7419119_earthworm-sense-light_.html
http://knol.google.com/k/unique-invertebrate-eyes#
Danielle Webb (dwebb456@gmail.com)
A sense is defined as "the physiological capacities within organisms that provide the inputs for perception" (Wikipedia). In other words, senses are the ways in which animals interact with the world, and how we perceive the world. We have different senses because the more information we gather from our senses, the more we are aware of our environment, and the better chance we have of surviving. Humans rely heavily on their sight, with over 80% of the sensory information given to the brain coming from our eyes. This is because of our five senses, our eyes are the most complex and well-developed. Our eyes, using the cone cells in our retina and the muscle cells in a process called "accommodation", can interpret the things in front of us with great detail without direct contact. When we touch or taste things, we have to be in contact with the object and even then we don't gain nearly the amount of detail as we do simply by looking at it. Our eye cells interpret the vibrations of light waves with remarkable detail, seeing much farther away than we can hear.
ReplyDeleteWe think that eyes originated as tiny patches of sensitive cells which responded very bluntly to light. As this was a new sense, it provided its organism with more information about its environment and gave it enough of an advantage to make that organism thrive. Over time, this patch of cells deepened and the opening to the tiny pit narrowed, forming the primitive shape of our eyes. Over time a lens was developed, probably from a thin film of liquid that eventually formed the present-day curvature. Eventually this formed our highly developed eye. We also see evidence of each step of this evolutionary process in modern day animals.
As organisms developed eyes, they started to rely more and more on their sight as opposed to their other senses. Humans rely overwhelmingly on their sight, and as Kyle said, this "provides...humans with a great evolutionary advantage". This is true for human environments, in which it was advantageous for us to survey our environment from farther away so we could hunt our prey and avoid our predators. However I disagree with Kyle when he says that other organisms are at a disadvantage by not having eyes like ours, and are "forced to use other senses". Those animals are not at a disadvantage, they just use different means to gain the same advantage. Sure, placed in an environment like ours would give us an advantage over, say, a bat because our eyes are more developed. However all animals are not in the same environment, which is the reason we see diversity of life. Bats environments have pressured them into forming a well developed sense of hearing, being capable of hearing about 5 times the range of frequencies as humans can. Were we placed in a bat's environment, we would not be so proud of our sight. Bats simply observe their world differently than we do, and it is not a disadvantage at all, otherwise we would not have bats anymore.
http://en.wikipedia.org/wiki/Sense
http://www.vision1to1.com/EN/HomePage.asp?BGColor=1&Category=6&Article=122
http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html
http://www.lsu.edu/deafness/HearingRange.html
Jeremy Solomon
imabum14@gmail.com
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ReplyDeleteWhile humans tend to only think about their own vision and eyesight, eyes work in all kinds of different ways, allowing some animals to see in ways that humans can only imagine.
ReplyDeleteLike many predators, owls have their eyes located together in the front of their face, which allows them excellent depth perception during their hunting expeditions. These massive eyes are fixed in their sockets and can barely move. This is why the owl can turn its head so far. Another organism with unique eyes is the Gecko. Nocturnal geckos have to be able to block out the bright sun during the day while still retaining excellent night vision, which is why they have long zig-zagged pupils that can tightly constrict to let in little light. On the other hand, humans cannot see colors in dim moonlight, these animals can tell the difference between colors and their eyes are calculated to be almost 350 times stronger when it comes to seeing color. Although the two following examples seem much different from the human eye, they are actually similiar in comparison to insect eyes.
Like most insects, butterflies have compound eyes, which are made of hundreds of microscopic, six-sided lenses that allow them to see in every direction simultaneously. While this type of vision prevents the bugs from seeing things in sharp focus, butterflies can see ultraviolet light, which is invisible to the human eye.
We can look into the evolutionary past of the eye to see exactly why different organisms have such different capacities for strong vision. Visual pigments appear to have common ancestry while complex image forming eyes seem to have evolved 50-100 times which can explain the complexity of eyes in different organisms. Complex eyes appear to have first evolved within a few million years during the time period known as the Cambrian explosion. The complete evolution of an eye like that of a vertebrate or octupus took about 2000 steps. In conclusion, the reasons for unique but yet still similiar eyes within similiar species is described in this response; and the differences between vertebrates and inverterbrates eyes is listed in the responses by Kyle and Jeremy.
Eryk Fundakowski- arthur2446@comcast.net
http://biology.fullerton.edu/deernisse/pubs/Serb_Eernisse_08.pdf
http://www.2think.org/eye.shtml
http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html
Organisms have developed different types of eyes over time. This ability to see proved advantageous and continued to future generations and has been carried on since. Eyes have been used for avoiding predators and scavenging for food and have hence been able to serve as an amazing guide in survival. Specific organisms such as insect and octopus are some of the few species to have evolved compound eyes. Unlike the single-lensed eyes of the vertebrates, compound eyes of flies and other invertebrates are composed of individual lenses called ommatidia. Each ommatidium that descends into the core of the eye has a complex structure. From the light hitting the different parts of the eye, a message is sent. As Jeremy mentioned, this message is sent from the eye to the brain where it is processed as an image.
ReplyDeleteCompound eyes have very limited range of vision, and can only see a short distance away. The vertebrate eye is able to see in great detail. An insect’s eye, though not as high of a resolution, is a selective advantage because it offers a greater rate of processing for animals that are used to being in flight. On top of all this, the invertebrate eye is also able to see at different angles than us, since we have “camera eyes” which create a blind spot.
Our eyes are better for us as humans, since we aren’t constantly in flight or fast moving like insects. Our eyes are able to see higher resolution and focus on objects. Being able to see vivid detail is something that humans have as an advantage. Over time, our eyes might develop even further, allowing us to see greater distances or greater detail, although our current state of vision is already impossible to achieve through evolution (http://www.gennet.org/facts/metro10.html).
Sources:
http://icb.oxfordjournals.org/content/43/4/508.abstract
http://wwworm.biology.uh.edu/evodevo/lecture24/gehring02.pdf
(Alex Sapozhnikov marijio@gmail.com)