Evolution

and natural selection

Hudson River has been polluted by one of the worst industrial chemicals

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PCBs

  • Polychlorinated biphenyls, otherwise known as PCBs were used in many commercial and industrial products in the late 1920s
  • General Electric released about 1.3 million pounds of PCBs into the Hudson River from 1947 to 1976
  • They were banned in the 1970s but they polluted major waterways and rivers around the world
  • A 200-mile stretch of the Hudson River is the nation’s largest Superfund site because of PCBS
  • PCBs dont degrade they keep polluting the environment for years and years
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Atlantic Tomcod

  • Researchers found they are able to live in the Hudson River even with the high level of PCBs
  • Scientists have found high amounts of PCBs in the stomachs of tomcods, that would normally kill them
  • The tomcods have evolved some kind of protection against the PCBs over the last 20 to 50 generations

What Changed?

  • Atlantic tomcod modified a gene encoding a protein which is able to then regulate the effects of the toxin as well as other chemicals, known as the aryl hydrocarbon receptor2 (AHR2)
  • Most fish have a receptor gene that contains a protein which regulates the effects of toxins.
  • The tomcods have that gene, but over the past few years, their version has dropped six base pairs, the part of the DNA that toxic molecules stick to.
  • PCBs do not bond very well to these receptors the effect of the chemical are reduced.
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  • They found that the mutation was present in 99 percent of the tomcods in the Hudson, compared to fewer than 10 percent of the tomcods from other waters

Cleaning the Hudson:

  • They are trying to clean up the Hudson River and are worried that the newly evolved Atlantic tomcod might not be able to manage as well without any PCBs in their bodies
  • The removal of the toxic chemicals will affect the fitness of the Atlantic tomcod of the Hudson River, resulting in another shift in the evolutionary pattern of this species.