Newswise — [Evolution of Cadmium Resistance in Daphnia magna; Environmental Toxicology and Chemistry], 2005; Vol. 24 (9):2341-2349

A study of the evolution of cadmium tolerance in Daphnia magna has shown what appears on the surface to be a survival enhancement. Upon further examination, however, the resistance developed may have the potential to reduce, rather than improve, the long-term survival of the adapted population. The results of the study are published in the latest issue of Environmental Toxicology and Chemistry.

Increased resistance to acute toxic effects of cadmium was observed over eight generations. No differences in survival, growth, fecundity or demographics were observed. Although not associated with reduced fecundity, cadmium-adapted daphnids were smaller, which could be ecologically significant and capable of affecting fitness. Also, it could indicate a trade-off between growth and detoxification ability.

Other observed changes were decreased genetic diversity and increased sensitivity to at least one other toxicant. The adapted population was less tolerant of phenol, though more tolerant of lead, than were unadapted populations.

Results from the Daphnia magna study have a wider application. Some organisms are able to survive and apparently thrive in contaminated habitats. The resistance of pests to pesticides and of pathogens to antibiotics has been widely reported. However, though these organisms may be surviving, they may not in fact be thriving, and they may be at increased risk from other stressors. Thus, survival of populations in contaminated areas may not be as positive ecologically as has been thought.

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Environmental Toxicology & Chemistry Vol. 24 (9):2341-2349 (Vol. 24 (9):2341-234)