Hudson River Fish Evolved in a Flash To Survive Polluted Waters

By Andrew Moseman | February 18, 2011 10:36 am

The Hudson River has been one of the most polluted in America, but because of that pollution, it’s now the site of evolution happening at a breakneck pace.

The furiously evolving species is the bottom-feeding Atlantic tomcod, which lives in areas of the Hudson that were contaminated by PCBs through much of the 20th century.

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. [National Geographic]

Despite swimming in PCB-polluted waters and accumulating the chemicals in their systems, the tomcods are alive and well in the river. In a study in Science this week, Isaac Wirgin and colleagues show that this is because in the span of just a few dozen generations, the fish have evolved a resistance to PCBs.

The resistance is provided by a variant in a single gene that prevents the chemical from binding onto cells in the fish, Wirgin explained.That variant, he said, is found in about 95 percent of the tomcod in the Hudson. It appears in about 5 percent of tomcod in two smaller streams in Connecticut and on Long Island, and “if you go further from the Hudson you don’t see it at all.” [Wall Street Journal]

The modified gene is called aryl hydrocarbon receptor2, or AHR2. PCBs have a difficult time binding to the mutated version of this receptor, which is caused by the tomcods missing six base pairs of DNA. What’s truly odd, though, is the speed at which the fish developed this trait—it took perhaps just 20 to 50 generations.

But while the tomcod evolution is an impressive feat, it’s not necessarily great news overall, nor does it get polluting humans off the hook.

For one thing, he and others said, the fish are probably paying a price for the mutation, something like slower growth or less resistance to other stresses. Also, the surviving fish are moving contaminants into the food chain. “They serve as a prime prey for striped bass,” Wirgin said. “You’ve got this fish that would normally be dead from PCBs or dioxin. It’s alive and it’s carrying around all this PCB and dioxin and it gets eaten.” [Discovery News]

Related Content:
80beats: Study: Lice-Infested Farmed Salmon Not to Blame for Wild Salmon Die-Off
80beats: First Marine Census Describes the Wonders–and Troubles–of the Seas
80beats: EPA’s Bright Idea: Let’s Get Rocket Fuel Chemical Out of Drinking Water
DISCOVER: 20 Things You Didn’t Know About… Water

Image: Science / AAAS

  • Eugene Leff PhD

    After reading the article I thought I can explain my interest in that matter.
    In 1964, 1965 and 1966, I was part of the team surveying the Hudson River for the NYU Dept of Environmental Medicine at Sterling Forest under Dr. Merrill Eisenbud.
    We seined both east and west shores of the Hudson from just north of the Tappan Zee Bridge to Saugerties, NY. The results of our survey (the first since 1937) was published.
    The Tomcod was one of the species collected by our team.
    I subsequently received my PhD from NYU in 1969 under Alfred Perlmutter and was a member of the American Fisheries Society as well as the Atlantic Fisheries Biologists.
    I am Professor Emeritus at QCC(CUNY).

  • Katie Cunningham

    The New Bedford Killifish! We meet again!

    I wrote a paper on this sucker, and it was actually what drew me into biology for the first time. I wish I still had the paper, as there was a great book on pollution and matters of degree in my resources :(

  • Village Idiot

    Am I missing someting?

    1) There is a sudden and deadly change in the environment.
    2) There is a very large breading population.
    3) The only individuals left breeding are mutants who have the ability to survive.
    4) Ergo=> A sudden genetic change in the population. These are not new genes. They simply changed from a distribution of 1 to 10^7 to 99% of the population.

  • Bob Snyder

    Your name suits you well, Mr. Village. I’m no biologist but isn’t that just what evolution (and natural selection) is? A previously unnecessary trait found in a small percentage of the population all of a sudden becomes favorable due to some environmental change (pollution in this case) and in a matter of x amount of generations later, that trait is now found in a larger percentage of the population due to natural selection? The point of the article is that it happened very quickly, though it would have been nice if they mentioned how long it usually takes for something like this to occur.

  • amphiox

    It is also unknown when this mutation first appeared in the population. The variant might well be a relatively new mutation, one that arose only after the fish began encountering PCBs.

  • Pippa

    Fascinating. Could we clean up the river and remove the pollutants from it by encouraging and then removing the chemical laden fish?

  • John Lerch

    re VIdiot’s and BS’s discussion. The article could have made it clearer whether this gene is or is not detrimental. If it is detreimental, then 1 out of 10^7 might be way too frequent–1 out of #=#particles of the universe might be more correct. If it is neutral under clean circumstances, then 1 out of 10^7 might be correct.
    Also the fact that this is a binding issue raises the spectre of Lamarckian evolution. The PCB binds to parts of the DNA causing the likelihood of deletions to rise.

  • Dikken

    Village, you are indeed missing something – populations of tomcod further away from the Hudson do not have the mutation, suggesting that it is a new mutation.

  • Gil

    @7 No lamarkianism involved; the article states that the PCBs bind to the receptor protein coded by the DNA segment, not the DNA segment itself.

  • amphiox

    Even if the PCBs (or any chemical pollutant) bound directly to DNA and directly caused DNA to mutate more frequently, it would not be Lamarckism, because those mutations will still be variable and random in their effect, and there will still be selection for the ones that are beneficial and against the ones that are not. Just having a mechanism that increases the mutation rate as a result of some environmental factor is not equivalent to Lamarkism, which is the inheritance to characteristics acquired through the use and disuse of parts.

    For this to count as even partly Lamarckian would require the PCB to bind specifically to the DNA in a way that always produces the deletion that confers resistance, and no other damage or mutation, and for these mutations in somatic cells to always somehow be transferred to the germ line so that it will always be inherited. Furthermore, the increase in the resistant trait in the population would have to result not from selection in favor of the resistant individuals, but from all those individuals who acquired the resistance in the previous generation passing it on to their offspring. The Lamarkian mechanism for evolution importantly does not include selection. If selection is involved in any way, it is a Darwinian process.

    Mutation -> Variation -> Selection -> change in population genetics is Darwinian no matter what was the cause of the mutation to begin with (and technically, if you think about, ALL mutations are acquired characteristics for the individual in which they first occur.)

  • amphiox

    4) Ergo=> A sudden genetic change in the population. These are not new genes. They simply changed from a distribution of 1 to 10^7 to 99% of the population.

    The important thing you are missing, VI, is that evolution does not require the addition of new genes. The vast majority of all evolution involves changes in the frequencies of genes that already exist, and which may have existed for a very long time. New genes appear from time to time and “join the party” so to speak (and old genes may “leave”). But the first appearance of a new gene is basically not a big deal. By definition, a new gene is very rare in the population, rare enough to be basically undetectable, with no impact on the population at large, and it will remain rare until something (usually selective pressure) acts on it to amplify it.

    It is the amplification of a gene that is the big deal when we talk about evolutionary change. The gene might be a new mutation, or it might have first appeared thousands or even millions of years (or generations) ago but remained at a very low frequency for all that time. Or it might even have appeared multiple times in the past but went on to die out because there were no selective pressures favoring it during those times.

    It doesn’t actually matter on bit where the gene came from or how long its been in the gene pool. A lot of the time there’s no way to tell either way.

    It is the change in the frequency of the gene that matters (and is, in fact, the actual DEFINITION of evolution).

  • Brian Too

    I’m confused. If the PCB’s are not binding to the (protein receptors?), then it would seem that there is no mechanism for them to build up in the fish. If that’s true then the comment that “…it’s carrying around all this PCB and dioxin…” makes no sense.

    Is there another way for the contaminants to build up? Are these fat soluble toxins?

  • stop evangelizing evolution

    Evolution?! This is a mutation at best. Those fish are not going to crawl out of the water and start walking because they don´t like the PCB´s. They are being affected by it and it´s as a result of poisoning. If you get poisoned by something that does not kill you, and maybe your offspring may have some funny defects which is visible / invisible. It´s simply mutation. You still have the same DNA, it´s just in the process where the body carries out the instructions of the DNA to construct the body where there comes a problem due to poisoning. There has also never been a beneficial mutation and evolution is still only a theory with no real proof.

  • Leopold Goyer


    To Stop Evangelizing Evolution: When do you think ”Those fish” __like you call them__ were created, 8 to 9000 thousand years ago?, (the Bible’s time, with mud and water) or 250 to 300 thousands years ago, the dinosaurs’ time (before Noah’s arch). and who created the Dinosaurs and families. With mud and water also?

  • cat epoxy

    This is what I have been seeking in a lot of internet sites and I finally found it here. Astounding write-up. I am so impressed. Could never ever assume of this kind of a matter is probable with it…I believe you have a good understanding in particular even though dealings with these kinds of subjects.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar