Just a Theory, Part 1,476,598

Rapid evolutionary change in the polluted Hudson River:

Bottom-feeding fish in the Hudson River have developed a gene that renders them immune to the toxic effects of PCBs, researchers say.

A genetic variant allows the fish to live in waters notoriously polluted by the now-banned industrial chemicals, and distinguishes the fish—Atlantic tomcod (Microgadus tomcod)—as one of the world’s fastest evolving populations. . . .

PCBs, or polychlorinated biphenyls, were first introduced in 1929 and were used in hundreds of industrial and commercial applications, mostly as electrical insulators. They were banned 50 years later, but they don’t simply degrade. Partly because of PCB contamination, a 200-mile stretch of the Hudson River is the nation’s largest Superfund site.

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. But until now, scientists have never understood how they survived PCB exposures that kill most other fish.

“Exposure of fish embryos to PCBs in the lab causes the heart to be smaller, to not beat properly,” Wirgin said. He and his colleagues suspected the fish harbored some sort of protection. They spent four years capturing tomcod from contaminated and relatively clean areas of the Hudson River during the winter spawning season.

It turns out the fish sport a handy modification to a gene encoding a protein known to regulate the toxic effects of PCBs and related chemicals, called the aryl hydrocarbon receptor2, or AHR2.

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.

Life is amazing.