Posted on 08/09/2003 5:52:47 PM PDT by forsnax5
Loss of evolved resistance to cadmium pollution in worm following a major habitat cleanup | By Stuart Blackman
Foundry Cove on the Hudson River was one of the most heavily metal-polluted areas in the world. Between 1953 and 1979, a battery factory released approximately 53 tons of cadmium (Cd) and nickel hydride waste into the cove, resulting in sediment Cd concentrations as high as 10,000 ppm. The cove's commonest invertebrate, Limnodrilus hoffmeisteri, an oligochaete worm, evolved resistance to the Cd, and its central position in the food web is thought to promote the transfer of the metal through the ecosystem. In the August 4, PNAS Jeffrey S. Levinton and colleagues at Stony Brook University report that L. hoffmeisteri has subsequently lost its resistance following a major cleanup of the site in the mid-1990s.
Levinton et al. measured the resistance of L. hoffmeisteri to Cd over a 9-year period (1993–2002) starting 1 year before the $100 million Superfund cleanup, which immediately brought sediment Cd concentrations down to less than 10 ppm. In the first year after the cleanup, resistant forms endured in the bay, but by 2002, the worms' ability to withstand exposure to Cd was indistinguishable from those in neighboring South Cove, an area unaffected by the pollution. Resistant worms grew more slowly than nonresistant worms, probably because of a diversion of resources into the production of large quantities of a metal-binding metallothionein-like protein. Such selection against Cd resistance in the absence of the metal resulted in the worm reverting to its nonresistant state in an estimated 9 to 18 generations and demonstrated the potential for ecological restoration to rapidly reduce the potential for the transfer of pollutants through ecosystems.
"Our study shows that environmental restorations may cause rapid genetic recoveries. Our results are consistent with a rapid recovery of resistance previously found when the insecticide DDT was relaxed against the mosquito Aedes aegypti," conclude the authors.
There's hope for the environment after all...
:)
Presumably, that would take more than 19 generations.
;)
And frankly, more evidence against a slowly changing stochastic process as an explanation.
Well, "slowly changing" certainly doesn't seem to apply to this example.
This article led me to look up the nature of cadmium and its effects. The stuff is toxic but not immediately lethal, and is naturally occuring in soil (albeit at lower levels than described in the article), so it would make sense that soil-dwelling creatures would have some existing level of defense against it.
I figure that the "non-resistant" worms normally have the basic ability to produce the metal-binding protein, some more than others. The ones with a stronger ability were able to cope with the rising levels of cadmium, and therefore able to pass on that level of ability to the next generation.
The rapid change would seem to indicate that the inate ability typically varies quite a bit between individuals.
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