| Development of mercury tolerance by the aquatic oligochaete worms Sparganophilus pearsei and Tubifex tubifex was studied S. paersei is commonly found in fresh water reservoirs around the San Francisco Bay Area, California. They are tolerant, sedentary, relatively long-lived, abundant, large, easy to sample and suitable for laboratory handling. Mercury is an abundant contaminant in San Francisco Bay Area watersheds.; The tolerances exhibited by different populations of S. pearsei were evaluated using laboratory experiments. It was found that there is a positive relationship between tolerance and mercury pre-exposure. The higher the concentration of mercury in native sediments, the higher the level of resistance observed in the worms in the laboratory. Two behavioral mechanisms involved in the development of mercury tolerance were studied: sediment avoidance and autotomy (a mechanism of mercury detoxification). The frequency of these behaviors increased with concentration of mercury and time of exposure.; Effects of contaminated sediments on the development of tolerance in tubificid worms were also studied. T. tubifex raised for several generations under mercury stress developed mercury tolerance that was still present after three generations without this stress. Worms from a reference group crossed with tolerant worms produced offspring with intermediate mercury tolerance. Thus, mercury tolerance in these worms can be genetically inherited, i.e., adaptation has occurred.; These results emphasize the importance of considering specific population tolerances of native endemic and cosmopolitan species during biomonitoring and toxicity testing. The demonstrated benefits of including sublethal as well as lethal endpoints in toxicity tests include a more realistic understanding of the impact of pollutants. Studies such as those conducted herein, with other species and other contaminants, would aid our understanding of why some organisms are able to flourish under conditions that appear inhospitable due to contamination, which others cannot. |
