Adapting to Toxic Environments

Many organisms have evolved tolerance to natural and human generated toxins. The most recent examples are killfish in some highly polluted Eastern rivers who have evolved to survive levels of toxins up to 8,000 times the lethal dose.

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The minnow-like Atlantic killfish spend their entire lives in a toxic stew of chemicals in some of the United States' most polluted waters. In four severely polluted East Coast estuaries, the fish have evolved with genetic mutations that leave them tolerant to normally lethal doses of industrial pollution, according to a study led by University of California, Davis researchers. (1) Killfish, sometimes called mud minnows or mummichog, are abundant in the brackish waterways and marshes along the Atlantic coast. They're an indicator species, one that is used as a barometer to gauge the health of ecosystems because they are typically really sensitive to pollution. Yet at some highly contaminated sites, scientists have found something unexpected. Killfish at these sites are extremely tolerant to some very nasty chemical pollutants. (2) There are a number of other examples of the amazing ability of nature to heal itself and adapt to situations we would think are unbearable. Evolution is usually thought of as occurring over long time periods, but it can also happen quickly. The 1964 Alaska earthquake made some parts of the Pacific into ponds on a few islands. Fifty years later the fish in those ponds are now freshwater fish. Apparently, the genes for dealing with this sort of wild extreme change are held by some of the fish and natural selection worked its wonders in a few decades. (3)

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Worms in Foundry Cove on the Hudson River are another example. Between 1963 and 1970 industry in the area dumped more than 100 tons of nickel-cadmium waste into the cove along with other toxins including arsenic and lead. As much as 25% of the cove's bottom sediment dwelling consisted of cadmium, which is highly toxic. Yet many bottom dwelling invertebrates were present in numbers no fewer than in unpolluted areas at other sites. Whereas local cove worms thrived and reproduced, worms from a nearly cove showed clear signs of distress, or died when placed in Foundry Cove. Yet offspring of Foundry Cove worms raised in clean muds were tolerant of cadmium, leading to the conclusion that genes were largely responsible for the tolerance. This degree of metal tolerance could have developed in just 2 to 4 generations, or a couple of years. (4) Other examples of this tolerance to toxins can be found in a previous report. (5) References

1. Noah M. Reid et al., “The genomic landscape of rapid repeated evolutionary adaptation to toxic pollution in a wild fish,” Science, 354, 1305, December 9, 2016
2. Lindsey Konkel, “These fish evolved to live in extremely toxic water,” nationalgeographic.com, December 8, 2016
3. Emily A. Lescak et al., “Evolution of stickleback in 50 years on earthquake uplifted islands,” PNAS, December 14, 2015
4. Jeffrey S. Levinton, “The big bang of animal evolution,” Scientific American, 267, 84, November 1982
5. Jack Dini, “Resiliency of nature- life adapts,” Canada Free Press, January 5, 2016

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