The Atlantic tomcod found in New York's Hudson River  (Source: Mark Mattson of Normandeau Associates, Inc.)
Having a variant AHR2 receptor gene has made the tomcod resistant to PCBs in the Hudson River, but it may have harmful effects

Scientists from the Woods Hole Oceanographic Institution (WHOI), the National Oceanic and Atmospheric Administration and New York University have discovered that a certain fish found in New York's Hudson River has lived and flourished through 50 years of extreme pollution. 

Isaac Wirgin, study leader from New York University's Department of Environmental Medicine, along with Mark E. Hahn, senior scientist at WHOI, and Diana Franks, WHOI biologist, have found that the Atlantic tomcod, a common fish found in the Hudson River, has not only survived mass amounts of pollution in this river for a long period of time, but has also thrived in this particular environment. 

It's common to see insects develop resistance to insecticides, or bacteria to antibiotics, but according to Wirgin, this is the first instance where a member of the vertebrate population has developed a resistance to a hostile environment.

The Hudson River has become polluted partially due to two General Electric facilities releasing 1.3 million pounds of polychlorinated biphenyls (PCBs) over a 30-year period. Now, 50 years later, the Atlantic tomcod is alive and better than ever, and researchers have pinned a single genetic receptor as the reason for the vertebrate's resistance. 

Researchers found that a receptor gene called AHR2, which mediates toxicity and controls sensitivity to PCBs, is what made the Atlantic tomcods evolutionary change possible in order to become resistant to PCBs. More specifically, the Hudson River tomcod's AHR2 proteins seem to be missing two of the 1,104 amino acids that are traditionally found in this protein, which weakens the bond between the receptor and the PCBs. Researchers believe this weak bond is what prevents the PCBs from affecting the tomcod in this area. 

With PCB resistance, the tomcod is capable of living in this area and reproducing in the winter. But when summer comes around, the tomcod becomes a prime food source for the striped bass and other fish. This is a problem because despite the tomcod's PCB resistance, the fish still absorb these contaminants and can pass them on to those that eat them. Through this transfer, humans who fish and eat what they catch from the Hudson River can consume the contaminants as well. 

This isn't the only negative aspect of the tomcod's resistance. According to researchers, this genetic change can make these fish more sensitive to other harmful chemicals like polycyclic aromatic hydrocarbons (PAHs) because the tomcod "cannot degrade them properly."

The AHR2 receptor is a normal part of development for the tomcod, but this type of genetic change that has made the tomcod resistant to PCBs in the Hudson River could have long-term harmful effects on the health of this fish. 

"Hudson River tomcod have experienced rapid evolutionary change in the 50 to 100 years since the release of these contaminants," said Wirgin. "Any evolutionary change at this pace is not a good thing."

Cleaning up the river wouldn't be a good thing for the fish either, because the fish would need to adapt to the cleaner environment once again, experiencing more fast-paced evolutionary changes. Researchers are currently unsure as to what these consequences are as far as long-term health goes for the fish during the evolutionary changes. 

Recently, an EPA-mandated cleanup of the Hudson River PCBs has begun, which may be troublesome for the tomcod who have developed a variant AHR2 gene specifically for the toxic substance. 

This study was published in Science.

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