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Evolution of cadmium resistance in Daphnia magna

Authors

  • Timothy J. Ward,

    Corresponding author
    1. Environmental, Earth, and Ocean Sciences Department, University of Massachusetts Boston, Boston, Massachusetts 02125, USA
    2. T.R. Wilbury Laboratories, Doaks Lane, Marblehead, Massachusetts 01945, USA
    Current affiliation:
    1. The current address of T.J. Ward is Gradient Corporation, 20 University Avenue, Cambridge, MA 02138, USA
    • Environmental, Earth, and Ocean Sciences Department, University of Massachusetts Boston, Boston, Massachusetts 02125, USA
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  • William E. Robinson

    1. Environmental, Earth, and Ocean Sciences Department, University of Massachusetts Boston, Boston, Massachusetts 02125, USA
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  • Contribution 402 from the Environmental, Earth and Ocean Sciences Department, University of Massachusetts, Boston, MA, USA.

Abstract

A diverse laboratory population of Daphnia magna Straus was established by combining individuals from eight sources. Artificial selection for increased resistance to the acute toxic effects of cadmium was performed, and after eight generations, the average median effective concentration increased from 61 to 180 μg/L. No differences in life span, offspring production, time to first brood, number of offspring in the first brood, or intrinsic rate of population increase (r) were observed between the cadmium-adapted population and the controls under ideal conditions or under conditions of temperature or feeding ration stress, but cadmium-adapted daphnids were smaller. Control and cadmium-adapted populations were equally sensitive to copper and malathion, but the cadmium-adapted population was less sensitive to lead and more sensitive to phenol. Analysis of amplified fragment-length polymorphisms indicated a significant decrease in genetic diversity in the cadmium-adapted population. Although the evolved cadmium resistance would allow adapted populations to exist in areas where cadmium concentrations would be toxic to unadapted populations, the decreased genetic diversity, smaller size, and increased sensitivity to at least one other toxicant could reduce the probability of long-term survival even in the absence of future cadmium exposure.

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