Saturday, March 26, 2011
The evolution of bones vs the evolution of cells
In chapter 4 of "Your inner fish," it mentions and explains the evolution of teeth to bones. Ostracoderms were the first animals found with bony structures that were made entirely from fused teeth. With the knowledge of how this occured, compare and contrast the evolution of bones with the evolution of autotrophic and heterotrophic organisms (Remember: Autotrophic organisms are believed to have formed after the heterotrophs). Include a reason for any possible similarities.
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During vertebrate evolution in freshwater, skeletal dissociation was a problem due to the calcitic skeletons. In response to this problem and greater phosphate concentration in the water, the skeletons of these vertebrates evolved to have a greater amount of phosphate in them (Ruben, J). The increase in phosphate concentration led to the evolution of hard bones. The calcium and phosphate concentration in the water in which the organisms were living was also important in determining how much of each element makes up part in the organism. The changing environment of this water, which included an increase in phosphate and a decease in calcium, along with the need to change the composition of the skeletons caused a greater phosphate concentration (Ruben, J).
ReplyDeleteHeterotrophs evolved before autotrophs did. The only means that the heterotrophs had to feed off of were “primoridal soup” and other early organisms (McDarby, M). As more food became available and cell cooperation increased, heterotrophs grew in cell number. New sources of food and environmental pressures also advanced heterotroph evolution (McDarby, M). Because autotrophs require oxygen from the atmosphere as well as light to undergo photosynthesis, they evolved much later than heterotrophs did. One reason for this could be that many years ago, the earth did not have as much light as it does now. Another possible reason is that oxygen levels were a lot lower many years ago than they are now. For this reason, autotrophs would not have the means to perform photosynthesis, which they need to produce energy to survive. There are clear similarities between the evolution of bones from soft skeletons and heterotrophs to autotrophs. In both cases, environmental conditions allowed for the organisms to use new resources (such as sunlight, oxygen, or phosphate) which allowed them to evolve and adapt more advanced features.
Sources:
http://www.jstor.org/stable/2409087?seq=4
http://faculty.fmcc.suny.edu/mcdarby/Animals&PlantsBook/History/07-Explaining-Life-on-Earth.htm
Marissa Lobl marissa.lobl@gmail.com
Marissa makes great points about the differences in soft and hard skeletons between the two trophic types, but she happened to skip over the role of autotrophic plants in this Venn diagram discussion of bone types. To elaborate, we learned in the Plant Diversity unit that plants utilize strong polysaccharides such as cellulose to build cell walls and photosynthesizing chloroplasts, a structure that animal cells happen to lack; this lack of cellulose could very well account for an animal cell’s greater necessity for stronger bones(Campbell 72). Relatively, no other type of cell can compare to plant cells in terms of strength and durability of outer cell membranes, except for the chitin used in arthropod exoskeletons, who are typically heterotrophs that survive off of plants and detritus (Campbell 74). However, consider that chitin and cellulose-utilizing organisms can be further categorized as small organisms that grow/live closer to the ground than other heterotrophs, so this could also account for their smaller and comparatively weaker bone structure. In addition to the evolution of heterotrophs to autotrophs via the development of sufficient oxygen in the Earth’s atmosphere as Marissa discussed, there are also significant differences in bone/teeth development during the evolution of eukaryotic cells (cells possessing a nuclear envelope-bound nucleus, complex DNA and sophisticated organelles like mitochondria) from prokaryotic cells (smaller cells possessing no nucleus, simpler structure and mobilizied flagellum); since eukaryotes tend to be much larger in size and could handle more complex functions than prokaryotes, this prepared eukaryotic organisms to have the advantage in developing teeth and bones, especially in those eukaryotes that were also heterotrophs (Source 4).
ReplyDelete(continued) Moreover, since Aparna asked about connections between teeth and bone development, it is important to remember that heterotrophs obviously need teeth to digest their primary producer/consumer prey, while most autotrophs do not even use their mouths to transfer energy from inorganic substances and light to the essential nutrients that they require. Since “the job of teeth is to make bigger creatures into smaller pieces”, autotrophs clearly lag behind heterotrophs in bone/teeth development because they don’t even feed off of such creatures (Shubin 60)! This even applies to so-called “carnivorous” plants such as the infamous Venus Fly Trap, which can be fertilized and nourished by decaying insects and organic parts; however, even though such plants are frequently mistaken to be autotrophs for their prey-seeking abilities, their successful survival in normal light conditions without involvement of insects still qualifies them as autotrophs (Source 3). To conclude, the higher up a heterotroph resides on their environmental food chain, the more necessity it has for strong, agile bone structure and efficient teeth in order to catch and digest their prey and fight off competitors; on the other hand, primary producers do not move to catch organic prey, and therefore do not require the same evolutionary advantages in terms of bones/teeth to capture the most amount of nutrients from photosynthesis/inorganic energy conversion.
ReplyDeleteSources:
1. Campbell
2. Neil Shubin
3. http://www.sarracenia.com/faq/faq1100.html
4. http://www.astro.wisc.edu/~townsend/static.php?ref=diploma-4#toc-The_Evolution_of_Autotrophs
Christine Lin
choco_cat11@comcast.net