On page 152, Neil Shubin mentions color and black and white vision. What evolutionary significance does color vision have to humans and why do some animals not have the ability to see in color? Other varieties of vision exist depending on the environment of an organism. Describe how vision varies between two of the followin: deep sea chondrichthys, Arachnids, a honeybee, a dog, and a human. Explain why each type of vision is key in the survival of the respective organism.
Yekaterina Khavkhalyuk (kittykatx93x@yahoo.com)
The reason humans have color vision ties all the way back to our ape relatives. Shubin described how color vision proved to be an evolutionary advantage shortly after he explained how vision works. The shift in receptors to allow us to see color may have changed when the flora in our earth changed. Color vision was a selective advantage for monkeys because when they lived on trees, the color vision “enabled them to discriminate better among many kinds of fruits and leaves and select the most nutritious among them” (Shubin 153). This happened about 55 million years ago and it is strongly believed that this was because the color of forests along with their food switched from monochromatic to a colorful one. The different coloring of food symbolizes different nutrition values, and obviously certain animals benefit from certain foods, therefore the monkeys with color vision had the advantage. After many generations, these monkeys were able to survive better than others because their food choices were healthier and better for them, and because of the environmental pressures and natural selection, they continued to survive and reproduce. Millions of years later, and now the entire human population (excluding those that are color blind) can see in color.
ReplyDeleteHumans have the same benefit as monkeys do when seeing in color. Because we are so closely tied to apes, we too need color for the same reasons. Of course now, with our ability to read and communicate, color vision isn’t the same necessity as it used to be, but as a result of our ape ancestors, we have color vision. Furthermore, Shubin described earlier that “we now rely on vision more than smell, and this is reflected in our genome” (Shubin 147). This shows that vision is one of the most important senses to us, superseding other senses.
Many animals cannot see color because they lack the receptor to see in color. The perception of color in humans is based on three types of cones, which some animals don’t have, not giving them the ability to see in color. “The three visual pigments [are] called photopsins” (Campbell 1102).
The vision in deep sea chondrichthyes varies. “Many cartilaginous fishes have vision adapted for low light, nocturnal activity or deep-water conditions, and poor color definition, and have retinas densely packed with rods and few cones. Some day-active sharks…have numerous cones as well as rods, and may have good color vision and high visual acuity” (http://www.biodiversityexplorer.org/chondrichthyes/senses.htm). The vision in arachnids, however, is completely different. Because their eyes spread in a circle, they are normally able to have 360 vision, but it is not very good. Some arachnids don’t even have any eyes! The ones that do, however, can only see blurs of color with little detail (http://www.bbc.co.uk/dna/h2g2/A2654714). The honeybee has a compound eye, which are made of hundreds of small simple eyes called ommatidia. They have a very large view angle and can detect movement very quickly. These insects have color vision and also can see into the UV spectrum. A dog has many rod cells (that allow them to see black and white), but few cone cells in comparison to humans, however they are able to detect motion better. “Dogs are said to have dichromatic vision -- they can see only part of the range of colors in the visual spectrum of light wavelengths. Humans have trichomatic vision, meaning that they can see the whole spectrum” (http://www.vetinfo.com/dogsee.html). And finally humans, which I have already mentioned in my above explanations, have the most complex eye out of all the other animals described. We are able to see color and detect movement well.
ReplyDeleteEach type of vision is key in the survival of each organism for clear reasons -- some organisms, like worms, wouldn’t need color vision because they don’t need to discriminate between food as much as humans need to. Dogs also don’t need color vision like humans do, instead, what is beneficial about their eyes is their ability to detect movement. Clearly each animal has their respective color vision based on their respective needs. If vision is not their primary sense, like it is in humans, then it is made up in other ways (for example, dogs have a superb sense of smell).
-Michelle Layvant, michellel94@hotmail.com
Invertebrates account for about 95% of known animal species on Earth. The massive variety of invertebrates means that there is a large amount of diversity among invertebrates since they have evolved for different conditions. Invertebrates are much older than vertebrates. The major phyla we studied are Cindarians, Calcarea and Siliceans, Platyhelminthes, Rofitera, Mollusca, Annedlida, Nematoda, Arthropoda, Echinodermata, and Chordata (Campbell 669). Each of these phyla is unique, but they also share common characteristics. All invertebrates have no spinal column or backbone, all are eukaryotic and don’t have cell walls. Without a backbone, most invertebrates cannot grow immense in size because they do not have the support and the nervous system requirements, although the giant squid is an exception. The giant squid also defies the fact that invertebrates are generally slow creatures because fast creatures need good support systems and a good oxygen delivery system, and most invertebrates have an open circulatory system, which wouldn’t work very well for that (Interesting Animal Staff 3).
ReplyDeleteVertebrates are different from invertebrates in many different ways. Vertebrates have neural crest cells, increased cephalization, a vertebral column, and a closed circulatory system for efficient energy exchange. All vertebrates also have a group of transcription factor genes called the Dlx family (Campbell 704). Because of the increasing complexity of vertebrate body plans, it can be inferred that a wider variety of genes started to emerge as well. The new genes probably emerged as a necessity because of the more complicated processes and the need for different proteins to be created through transcription and translation of mRNA.
There are similarities between vertebrates and invertebrates as well, although there are very few. Both can move, both are heterotrophs, both reproduce sexually, and both are found in a variety of environments. Besides this, there aren’t many similarities since there are 23 invertebrate phyla (Campbell 666).
Unique to invertebrates is the gastrovascular cavity, which is a sac with a central digestive compartment. This is used to digest food and also to excrete wastes. It functions as both an anus and as a mouth (Campbell 671). Also unique to invertebrates is an open circulatory system. Arthropods have open circulatory systems. For example, insects use tracheal tubes to absorb oxygen form the air. The air is then absorbed by the blood, or hemolymph, of the insect. The blood throughout the insect is partially oxygen-rich and oxygen-poor. Also unique to insects are the Malphigian tubules. These remove wastes from the hemolymph.
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ReplyDeleteOne ability unique to vertebrates is the increased ability to regulate systems. Vertebrates maintain homeostasis through a variety of unique mechanisms. Some use countercurrent exchange to maximize the diffusion of oxygen and carbon dioxide. Countercurrent exchange means that blood flows in opposite directions to exchange heat, keeping the oxygen-rich blood and oxygen-poor blood at similar temperatures (Thompson 7).
These mechanisms were developed in response to stimuli throughout the history of these animals. As a result, the animals with a certain selective advantage would survive and pass on their genes, and the gene pool would be slightly “improved” for the living conditions that the population lived in. Over time, these traits became exaggerated, and eventually became selective advantages for the species, so the species survived better with this trait, and the trait was passed on more and exaggerated more until the entire population had the trait. This evolution of certain traits are necessary to survive because of the constant stresses put on animals by the environment and other animals. Without constant adaptations, many species of animals wouldn’t be able to survive.
benitorosenberg12@comcast.net
http://www.interestinganimals.net/characteristics_of_invertebrates/characteristics_of_invertebrates.html
http://163.16.28.248/bio/activelearner/44/ch44c6.html