In the end of chapter 10, Shubin briefly describes the presence of both Pax 6 and Pax 2 genes in box jellyfish. These genes have the effect of creating pits all over the jellyfish that function as they eyes and ears. Why would it be helpful to have more than one pit of Pax 6 and 2?
aparna.pal.1994@gmail.com
Aparna Pal
While pax 6 functions in the formation of eyes, pax 2 helps develop the inner ear (Shubin 172). more of these genes would allow more receptors for light and sound waves. Animals such as jellyfish that have this advantage would be more keen to any predators lurking near by. Because jellyfish have radial symmetry, having structures that resemble eyes and ears would allow them to detect danger from any direction. The quicker that danger is discovered, the more time the organism will have to escape in order to survive and reproduce.
ReplyDeleteAccording to Shubin, "a link between Pax 2 and Pax 6 suggests that ears and eyes might have had a very ancient common history" (Shubin 172). It has also been found that "Pax 6 function in the developing eyes and central nervous system of vertebrates" (http://www.mdanderson.org/education-and-research/departments-programs-and-labs/labs/halder-laboratory/publications/callaerts-annrevneurosci-1997.pdf). More pits of pax 6 and pax 2 would lead to a more developed central nervous system. These organisms have the advantage of quickly detecting prey as well as their predators. Quicker capture of prey allows those organisms with more pax 6 and pax 2 genes to have a higher survival rate. For example, starfish have one eyespot on each of its rays (usually 5). Because they can “see” from multiple directions, they can quickly spot prey such as bivalves. Bivalves don’t have as many eyes nor are they as developed, so they can only detect when a shadow falls over them. However, by the time the starfish’s shadow covers the bivalve, it is usually too late for it to escape, therefore letting the starfish win the battle for survival.
Claire Yao (claire.yao521@gmail.com)
As Claire said, the Pax 6 gene functions in the formation of eyes while the Pax 2 gene helps in the development of the ear. Having more of both of these genes would help develop an animal’s light receptors and sound wave receptors. This would help develop the animal’s eye sight and hearing. In the jellyfish described on page 172, the Pax 6 and Pax 2 genes were almost combined to form the eyes. The jellyfish had many eyes, “more than twenty of them” (172). This would be advantageous to the jellyfish because they would be able to sense nearby predators more efficiently, as Claire said. Because jellyfish have radial symmetry, they also have a nerve net which serves as their nervous system. This nerve net allows the jellyfish to respond to its environment; however, it doesn’t give the animal any indication of where the stimulus is coming from. So, having the multiple pits of the Pax 6 and Pax 2 genes helps the jellyfish to be able to know where the stimulus would be coming from. This is a selective advantage for the jellyfish and other radial symmetric animals because they would be able to respond quicker to their predators, as Claire stated. Animals without eyes, or with fewer eyes, do not have this same advantage. Organisms like the bivalves, as Claire pointed out, don’t have as many eyes and so they are not able to detect their predators as quickly as animals with the increased amount of the Pax 6 and Pax 2 genes. So, in general, it would be helpful for animals to have more than one pit of Pax 6 and Pax 2 because it would help to decrease the amount of animals being caught by their predators due to increased sensory receptors.
ReplyDeleteSources:
http://www.jyi.org/volumes/volume1/issue1/articles/friedman.html
http://icb.oxfordjournals.org/content/47/5/712.full
http://en.wikipedia.org/wiki/Nerve_net
Danielle Webb (dwebb456@gmail.com)
Like both Claire and Danielle pointed out, "just like Pax 6, which we discussed earlier in connection with eyes, Pax 2 in ears is a major gene, essential for proper development" (Shubin 172). The combination, or "mosaic," of these genes in jellyfish result in the development of more than twenty eyes that are spread over the jellyfish's epidermis. Having both of these genes would develop the animal's eye sight and hearing,a selective advantage for this predator. As Danielle mentioned, jellyfish have a nerve net which serves as their nervous system and can simply be described as a loose network of nerves located in their epidermis. Although this does help the jellyfish detect various stimuli including the touch of other animals, which then transmits impulses both throughout the nerve net and around a circular nerve ring, the addition of the Pax 6 and Pax 2 genes would give jellyfish additional sensory organs to detect prey without the need to physically touch them.
ReplyDeleteThe big idea around these two genes, however, which Clair and Danielle perhaps briefly mentioned, is that the "major genes that control our eye and ear correspond to a single gene in more primitive creatures, such as jellyfish" (Shubin 172). This connection between our eyes and ears has been somewhat maintained, since we can see that a number of human birth defects affect both the eyes and the inner ear, according to Shubin. From jellyfish, it has been suggested that the "ancestor of jellyfish PaxB, a PaxB-like protein, was the primordial Pax protein in eye evolution and that Pax6-like genes evolved in triploblasts after separation from Cnidaria, raising the possibility that cnidarian and sophisticated triploblastic eyes arose independently" (http://www.ncbi.nlm.nih.gov/pubmed/14602077). This shows another step in the evolutionary pathway from the eyes of jellyfish to the eyes humans have today. Overall, this is simply another reflection of our connections to primitive creatures like the jellyfish.
Hannah Kay (hgkay@aol.com)
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