Question

Explain/define/comment upon the following item, making sure to define terms and addressing toxicity or other environmental aspects of the subject

. Another recent Science article indicates that tomcod (fish) in the Hudson River in New York State have developed some resistance to the toxicity of PCBs (very abundant there). Among their findings is that the aryl hydrocarbon receptor in the livers of these fish does not bind PCBs or TCDD nearly as easily as the same receptor does in the same fish in a PCB uncontaminated environment.

Answer 1

Atlantic tomcod (Microgadus tomcod) is one of the world’s fastest evolving populations.The 10-inch Atlantic tomcod has thrived despite the exposure to PCBs, and levels of the chemical in the livers of these fish are among the highest reported in nature.

The aryl hydrocarbon receptor2, or AHR2 genes regulates the toxic effect of PCBs. The fish are missing six base pairs of DNA of the AHR2 gene, and the two amino acids each triplet would code for. PCBs bind poorly to the mutated receptors, apparently blunting the chemicals' effects.

Hudson Bay tomcod had the mutation at least to a low degree before the PCB onslaught. In a classic case of natural selection, the fish with the mutated genes survived.
Cleanup might not be best for tomcod. That’s because evolutionary theory predicts a genetic mutation like theirs could render them compromised in some other area of their biology, and perhaps not well adapted to life without PCBs.