Sonali Deshpande
Mr. Mathieu
Period 2
Jan 14, 2014
Author: Carl Zimmer
Published: Jan 8, 2014
Article: http://www.nytimes.com/2014/01/09/science/a-living-time-capsule-shows-the-human-mark-on-evolution.html?module=ArrowsNav&contentCollection=Science&action=keypress®ion=FixedLeft&pgtype=article
Summary:
Scientists have found the South Center Lake in Lindstrom, Minnesota, from which they have been able to resurrect organisms that are up to 700 years old.This lake was chosen because its chemistry has been documented for decades, which makes it easier for scientists to observe how changes in pollution affect the organisms. The tiny shrimp-like creatures are known scientifically as Daphnia, or more commonly, as "water fleas." In the fall, some species of these produce heavily-cased eggs that fall to the bottom of the lake; some hatch in the spring, while some get buried under the sediment. Dr. Lawrence J. Weider, an evolutionary ecologist, had figured out how to coax these eggs to hatch in the mid 1990s. In 2009, to gather eggs to resurrect, his colleagues and he pushed a tube three feet into the sediment of the lake-- the oldest eggs he had resurrected were surprisingly 700 years old. To date the eggs, the scientists measured levels of the radioactive isotope lead-210, and are now confirming the dates with another isotope: carbon-14.
Then, scientists determined that in the late 1800s, there was a dramatic shift from a lack of phosphorous in the lake to an abundance of phosphorous. This was due to the fertilizer running off from new, local farms. Coincidentally, a previously rare strain of water fleas took over the lake as this increase in phosphorous occurred; because of the excess phosphorous, this particular species did not feel the need to waste their energy feeding on phosphorus. The resurrected fleas, however, did need to feed on it in their time because of the lack of phosphorous.
Connection:
This article connects to our unit on evolution. Lamarck had the idea that organisms adapt to their surrounding environments and niches, which is the case for the water fleas. When there was a lack of phosphorous, they saved it, and when there was an abundance, the water fleas simply disregarded it. This article also relates to Darwin's idea of "survival of the fittest." Though this research has nothing to do with competition, it can be inferred from the article that the newer strain of water fleas was more biologically "fit" than the resurrected species. Since they had did not have to use their energy on saving phosphorous, they had more energy than the resurrected fleas to survive to reproductive age, and more importantly, leave offspring. Another topic we learnt, genetic drift, the change in a gene pool by chance, was demonstrated when another species of water fleas took over. Finally, the dating of the Daphnia eggs relates to the radiometric dating--measuring radioactive isotope levels--explained in Chapter 15. An isotope's half-life is the number of years it takes for 50 percent of the original sample to decay. Since the Daphnia are relatively young in terms of the geological time scale, scientists would not have to use radioactive isotopes with long half lives. As radiometric dating is used mainly for rocks and fossils, they probably measured the ages of the rocks around the eggs. The article also mentions carbon-dating, which was talked about in the book as a method of dating recent fossils.
How were the scientists able to resurrect the 700 old eggs; wouldn't the DNA inside the nucleus be deteriorating and not functioning?
ReplyDeleteThe article simply mentioned that "some of the eggs were in good shape." As resurrection is not a common occurrence in biology, I was not able to find a clear answer as to how it actually worked. All I came across was that Lawrence J Weider used special technology, which was not actually defined. I would guess that the eggs were buried in a place where bacteria and fungi could not decompose the corpse, especially with their heavy casing. Though it doesn't explain how they didn't die, it shows that if cells had frozen, they would not have been decomposed.
DeleteWhy would the rare strain of water fleas neglect feeding on the phosphorus if it was an abundant source of gaining energy; "food"?
ReplyDeleteThe only reason the first strain fed on the phosphorous was because it was the only way for them to have enough phosphorous to survive, and if the supply ran lower than usual, they would have consumed some anyways. The rare strain did not have a need to consume the phosphorous-- they had other things to consume, and the phosphorous was already readily available in the lake.
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