Evolution in a toxic world

How life responds to chemical threats

Killifish, an oxymoron? Evolution of resistance to PCBs, dioxins and others.

Image of Fundulus heteroclitusOver the years, Diane Nacci and her group at the Atlantic Ecology division of the EPA, has done some really nice (and tedious) work with many populations, and generations of killifish which strongly suggests evolution in populations along the Atlantic coast, in response to PCBs, dioxins and similar acting chemicals. For a review of Diane’s work see: Adaptation of the Estuarine Fish Fundulus heteroclitus (Atlantic Killifish) to Polychlorinated Biphenyls (PCBs)

Additional studies with  Andrew Whitehead at Louisiana State University provide some insight into the mechanism behind such widespread resistance as discussed here. For more, see Common mechanism underlies repeated evolution of extreme tolerance to pollution, published in the Proceedings of the Royal Society B.

Also, Whitehead and others tease apart differences in gene expression associated with plasticity versus adaptation. In their article “Functional genomics of physiological plasticity and local adaptation in killifish” published in Journal of Heredity, 2011, 102:499-511.  In killifish, tolerance to rapid changes in salinity (e.g. saltwater populations transferred to freshwater) hundreds of genes respond, according to the authors, enabling fish to undergo  “early crisis contol phase followed by a tissue remolding phase.” Yet these changes are drawn from the existing genetic architecture, and as such are considered to be the result of a plastic phenotype. In contrast, resistance or tolerance to contaminants like PCBs and dioxins as discussed above, are the result of changes in the genome which are heritable and which have become fixed within exposed populations. Changes in salinity are thought to be sporadic in contrast to anthropogenic contamination like PCBs and dioxins, which are continuous for local populations, presenting perhaps differences in “spatial and temporal scale[s] at which environmental extremes ae experience in the lifetimes of individuals. For more see: Whitehead et al., 2011.


2 thoughts on “Killifish, an oxymoron? Evolution of resistance to PCBs, dioxins and others.

  1. Would this evolution of resistance mean increasing levels of PCBs over time in fish moving up the food chain, and concentrating in the longest-lived organisms (i.e. people)?

    Is there anything in the past rate of change comparable to the rate of new chemicals being introduced currently? Any suggestion of interaction effects in the paleo history, or were the newly appearing toxins so widely separated in time that each had an uncomplicated interaction with the then living species?

    1. Hi Hank thank you for your questions.

      Those are really some really good ones – and wish I had some good answers. As for your first one, at least, I can say that fishes managing to accumulate lots of PCBs are like high energy packets of food, laced with contaminants. So I think yes, these fish that increasingly tolerate PCBs and the like may aid in concentrating these kinds of chemicals up the food web.

      I’ve tried to think about past rates of change in the chemical environment. Some big ones are oxygen and then the ensuing change in available metals – but that certainly didn’t happen over a mere hundred or so years – so, as you point out – life adapted. I’d guess there have been many examples of local change which happened quickly (after a fire or volcano or those sorts of things – but they tend be acute and, not exactly “chemical” though I would guess there are changes in the chemistry of the local environment after those kinds of events – and there are species adapted for fire events etc.) And maybe a geologist can come up with some good examples of rapid chemical change on what would be a “microscale” of time – but I don’t know. With today’s contaminants, we are talking about changes that are slow and chronic for fast reproducers and somewhat acute for slow reproducers like us. So it’s not really surprising that many species adapt rapidly — particularly if they have short reproductive cycles (a year or two, or less.)

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